A Beginner's Guide To Plant Fertilizers

Inactive User
  • #1
There are many excellent articles, guides and threads on aquatic plant fertilisers here at FishLore, on planted tank, thebarrreport.com, aquaticplantcentral.com and advancedplantedtank.com. The aI'm of this guide isn't to replace these resources, but to collate a comprehensive range of useful information in a way that's accessible for beginners; to cover the most popular methods for dosing ferts; and to address some common aspects of fert use that aren't immediately apparent.

  1. Macronutrients and micronutrients
  2. Choosing a fert dosing method
  3. All-in-one ferts
  4. Estimative Index (EI)
  5. EI for low tech tanks
  6. Perpetual Preservation System (PPS-Pro)
  7. Iron ferts
  8. Flourish macro ferts
  9. Fert dosing calculators
  10. DIY dosing calculations
  11. DIY fert solutions
  12. Carbon intermediaries
  13. Substrates and substrate fertilisation
  14. Example of fert dosing regimens
1. Macronutrients and micronutrients

All plants require macronutrients (often called macros or NPK) in significant amounts, and these include nitrogen (N), phosphorus (P) and potassium (K).

Both nitrogen (in the form of nitrate NO3) and phosphorus (in the form of phosphate PO4) occur within aquariums as a result of the nitrogen cycle and the decomposition of excess fish food. Likewise, potassium is often found in trace quantities in tap water.

In addition, plants require micronutrients (sometimes referred to as micros and/or trace elements) in lesser amounts. These include iron, magnesium, calcium, sulfur, copper and several other elements. Many of these are found in tap water.
Note: The categorisation of nutrients as either a macro or a micro sometimes varies. For example, some resources consider magnesium, calcium and sulfate macros.
Even though many of these nutrients (both macro and micro) are present in aquariums as a result of using tap water and other chemical processes, usually it is the case that most of these are not found in significant quantities to assure good plant growth. In the vast majority of tanks, dosing fertilisers (commonly abbreviated as ferts) is necessary.

Carbon is sometimes considered a macronutrient as plants typically comprise up to 60-70% carbon. However, in planted tank fert dosing, sources of carbon are in most cases not listed as ferts because its main source is in the form carbon dioxide (CO2). Some products, including Excel and Metricide 14, can be dosed to supply carbon intermediaries. This is are examined in more detail in section 12.

2. Choosing a fert dosing method

There are a number of informal and formalised methods of dosing ferts, including (but not limited to):
  • All-in-one ferts
  • Estimative Index (EI)
  • Perpetual Preservation System (PPS)
Note: These are not the only methods available, but these are the most prominent in North America and other English-speaking countries (Australia, New Zealand, etc.). Other methods, such as ADA, can be found commonly in Europe and Asia.
The difference between these methods is related to the input ferts (whether it is a premixed solution or a dry fertiliser compound); how much of each fert to dose; and how often ferts are to be dosed. Because of these differences, choosing between one of these methods for a beginner can be a bewildering decision. This is especially the case when trying to decide between a nutrient rich method such as the EI method compared to a nutrient lean method such as PPS.
Note: Because most all-in-one ferts are quite dilute and their dosing recommendations very conservative, most would be considered nutrient lean. NilocG Thrive is one exception because of its concentrated formulation.
These and other differences arise mostly because of competing (and in some cases, mutually exclusive) understandings of plant biology and how nutrients are best apportioned in aquariums to elicit good plant worth while minimising undesirable effects (such as algae). This guide won't seek to explain the differences in depth due to the relative complexity (and contested nature) of the underlying theory. Aquarists are instead encouraged to read the 'Which Dosing Approach?' article at advancedplantedtank.com as an example of one way to differentiate across methods of dosing. In addition, planted tank has historically been dominated by EI dosing, while aquaticplantcentral.com has a higher proportion of PPS users.

For a beginner all of the above methods work well and can provide the necessary footing to become acquainted with ferts and other aspects of planted tanks. Because the input ferts are largely the same across EI and PPS (and any additional ferts can often be purchased affordably), switching between methods is simple if one should choose to do so in the future.

It is important to note, at this stage, that both EI and PPS rely on a well planted tank with sufficient plant biomass: simply having one Cryptocoryne and a few patches of Taxiphyllum barbierI 'Java moss' isn't likely to work well. A very lightly planted tank is better served by the conservative use of an all-in-one fert (see section 3 directly below).

3. All-in-one ferts

There are several aquarium-specific all-in-one ferts available which combine both macros and micros in a single mix. Most (if not all) are in the form of a liquid solution that is added directly to the tank's water column.

Many of these products are very dilute, and the bulk of the fert is simply a water solvent to the effect that one is mostly paying for water when purchasing these products. In addition, many contain little (if any) nitrogen or phosphorus based on the assumption that the aquarist's tank has a sufficient bioload such that nitrate and phosphates need not be dosed. This may not be the case for every tank, and many planted tanks typically have a low bioload due to aquascaping requirements.

The most useful all-in-one fert is NilocG Thrive, which is both comprehensive (all macros and micros) and concentrated. Thrive has a guaranteed analysis for its chemical composition and moreover, the fert's proportion of nutrients and recommend doses are structured according to the requirements of the Estimative Index (EI) method of dosing. Few competitor products offer a comprehensive listing of the solute nutrients in the fert.

The advantage in using a product like Thrive is that it is (1) easy to understand; and (2) easy to use, both of which are useful for beginners. It is particularly useful for very lightly planted tanks where using either EI or PPS may cause issues.

The disadvantage is that it's (1) unable to increase the dose of an individual nutrient in response to a particular deficiency; and (2) less cost-effective compared to using separate dry chemical fertilisers (which are often called dry ferts).

One caveat in using Thrive is that because of high fert concentration, it isn't especially best practice to follow the dosing instructions if your tank is very lighted planted as the recommend doses and frequency of dosing are structured according to high light, CO2-injected, well planted tanks with a low bioload. In moderately planted tanks with low light and no CO2 injection, it's better to use 1/2 of the recommended dose (1 pump per 20 gallons instead of 1 pump per 10 gallons) once a week (instead of 2-3 times a week). For very lightly planted tanks, it is recommended to use 1/2 of the recommended dose once every 1-2 weeks.
Note: Flourish is sometimes called Flourish Comprehensive to avoid confusion with other Flourish products. Despite its informal name, it is not a comprehensive, all-in-one fert. It has a distinct lack of macros and is best used as a micro fert. See this sticky thread by Mak for further information.

4. Estimative Index (EI)

The Estimative Index (EI) method of fert dosing was developed by Tom Barr, a noted planted tank expert who frequently contributes to the community at planted tank and thebarrreport.com.

The underlying principle of the EI method is the non-limitation of nutrients: all nutrients are dosed in excess to prevent a deficiency occurring for any given nutrient. Excess nutrients are removed through regular water changes. This is coupled with adequate lighting and sufficient CO2.
Note: Excess ferts (whether it is phosphate or another nutrient) will not cause algae issues in a well planted tank dosed with the EI method (or any other method, such as PPS).

It is the general consensus that algae growth in planted tanks is primarily due to poor plant growth and/or poor maintenance. An excess of dead/dying plant matter and a failure to undertake routine pruning/replanting/vacuuming causes an excess of carbohydrates and other organic compounds that triggers the growth of algae.

Combating algae is then a process of assuring good plant growth (either by sufficient ferts, lighting or CO2) and regular tank maintenance
The EI method typically uses dry ferts, the primary compounds being:

1. Potassium nitrate (KNO3)
2. Monopotassium phosphate (KH2PO4)
3. A micro fert mix, such as Plantex CSM+B or Flourish
4. Potassium sulphate (K2SO4) (optional)

Dosing K2SO4 is optional, as both KNO3 and KH2PO4 will generally supply adequate amounts of potassium when dosed according to recommended quantities for nitrate and phosphate.

On some occasions, when a tank's nitrate and/or phosphate levels are in excess without ferts (due to an elevated bioload and/or high feeding frequency), neither KNO3 or KH2PO4 are necessary. In which case, K2SO4 can be dosed separately as a potassium fert. K2SO4 can also be used with KNO3 and KH2PO4 in the case that potassium deficiency is observed in plants.

In addition, many planted tank aquarists dose an additional iron fert separately from their micro fert mix. This is discussed separately in section 7.

The following are the nutrient ppm targets for a high light tank injected with 25-35 ppm CO2 (often referred to as a high tech tank):

NO3: 5-30 ppm
PO4: 1-3 ppm
K: 10-30 ppm
Fe: 0.2-0.5 ppm

These targets are offered as a guide and the majority of people will adjust their individual fert doses in response to observations of plant growth. The adjustability of EI is important as no two tanks are alike in their nutrient uptake. As example, because of the density of fast-growing, stem plants in my planted tank, I routinely dose 4-5 ppm of PO4.

In order to reach the lower threshold of these targets, the following doses are required per 5 gallons:

KNO3: 154.67 mg (5 ppm NO3 and 3.15 ppm K)
KH2PO4: 137.22 mg (1 ppm PO4 and 0.46 ppm K)
Plantex CSM+B: 58 mg (0.2 ppm Fe) or Flourish : 1.2 ml (o.2 ppm Fe)
Note: As iron is the micro required in the highest concentration, it is typically used as the benchmark for determining micro fert mix doses: it is assumed that other the other trace elements in the micro fert mix will be present in necessary amounts when adequate iron is dosed.
Under a high tech tank environment, these quantities are dosed three times a week, with a 50% water change at the end of the week. Macros (KNO3 and KH2PO4) are dosed on alternate days and are dosed separately from micros (Plantex CSM+B or Flourish). For example, macros may be dosed on Monday, Wednesday and Friday; micros dosed on Tuesday, Thursday and Saturday; and a water change is completed on Sunday.
Note: Micros and macros are dosed separately in order to limit the reaction between iron and phosphate. However, as concentrations of both nutrients in typical aquariums with EI dosing remain relatively low, the extent of precipitation into ferrous phosphate is generally minimal even if dosed together. As a point of comparison, iron and phosphates are dosed together daily under the PPS-Pro method.
It is highly recommended to read section 7 regarding the use of iron ferts for more complete information about their use.

5. EI for low tech tanks

Low tech tanks are generally those that have low lighting and are not injected with CO2 (sometimes Excel or Metricide 14 may be used as a carbon supplement). The recommended fert doses listed above for high tech tanks can be adjusted for these low tech environments.

Rather than dosing 100% of the recommended dose three times a week, instead dose 50% of the recommended dose once a week. Instead of 50% water weekly water changes, opt for 10-25% weekly or fortnightly.

Over time, in response to plant growth, dosing may be increased from 50% to 100% of the recommended dose while maintaining the once per week dose frequency). If either Excel or Metricide is used daily, then one may dose immediately begin to dose 100% of the recommended doses once per week.

6. Perpetual Preservation System Pro (PPS-Pro)

To be updated.

7. Iron ferts

The iron present in micro ferts is generally chelated. That is, the iron is bound to chelating agents in order: (1) to improve its solubility in water; (2) to improve its biological availability to plants; and (3) to reduce the reactivity of iron to other elements/compounds in the water column (typically phosphate) which causes it to oxidise or precipitate into a form (such as ferrous phosphate) that is biologically unavailable to plants.

Chelating agents include the compounds EDTA, DTPA and EDDHA. The main distinction in use for planted tank aquarists is the stability of chelating agents at different pH levels. All iron chelates are stable at different pH ranges, with increasing alkalinity causing the iron to dissociate from the chelating agent and then becoming unavailable for plant uptake.

The following is an approximate comparison of the percentage of iron that remains chelated at different pH levels with different chelating agents:

EDTA iron chelate:
6.0 pH, 100% of iron chelated
6.5, 50%
7.0, 10%
7.5, 5%

DTPA iron chelate:
7.0 pH, 100% of iron chelated
7.5, 50%
8.0, 30%

EDDHA iron chelate:
11.0 pH, 100% of iron chelated

The iron present in Plantex CSM+B is chelated with EDTA. For those tanks where the pH is regularly at or above 7.0 pH, DTPA iron chelate is generally required to supplement Plantex CSM+B. Some aquarists routinely dose two or three times the recommended dose of Plantex CSM+B if their pH is at or slightly above 6.5 pH in order to provide sufficient iron. However, it is not recommended to dose Plantex CSM+B in proportions higher than this as there is vague anecdotal evidence that sufficient excess concentrations of other trace elements can cause toxicity issues. In addition, it isn't a particularly cost effective practice.

In general, few micro ferts contain DTPA iron chelate, so it will often need to be purchased and dosed separately. In addition, while EDDHA is most stable at the widest range of pH, it is not recommended for use in planted tanks due to its cost and tendency to stain tank water.

It is important to note that the iron in Flourish (and in Flourish Iron) is in the form of ferrous gluconate. While it is highly available for uptake by plants, it is also highly unstable and will generally become less available for plant uptake within 24 hours. Because of this, ferrous gluconate-based ferts need to be dosed daily. As with Plantex CSM+B, it is not recommended to dose Flourish daily due to vague anecdotal evidence regarding toxicity of other trace elements at excess concentrations (it also isn't a cost effective practice). Instead, it is recommended to use either Flourish Iron or EDTA/DTPA iron chelate (depending on tank pH).

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  • Thread Starter
  • #2
8. Flourish macro ferts

Many people using the Flourish micro fert mix will at some point purchase the Flourish macro ferts in Seachem's range: Flourish Nitrogen, Flourish Phosphorus and Flourish Potassium. It is certainly possible to dose the EI and PPS-Pro methods using Flourish products, but I do not recommend this. The Flourish macro ferts are very diluted: as an example, 1,000 ml of Flourish Phosphorus contains only 4.5 grams of monopotassium phosphate. Because of this, it becomes highly cost prohibitive with greater tank volumes on account of the increased dosing requirements .

Let us take a high tech 30 gallon planted tank as our reference point. The $15 EI ferts package (1 lb each of KNO3, KH2PO4, K2SO4 and Plantex CSM+B) from Green Leaf Aquariums will last 3 years and 7 weeks before needing a replacement (KNO3 will be used up first). According to prices on Amazon as of writing, the cost of using Flourish ferts (comprising five separate Seachem products: Flourish, Iron, Nitrogen, Phosphorus and Potassium) for our reference tank across the same length of time - 3 years and 7 weeks - will be approximately USD590.56.

Using dry ferts is a savings of over USD575. There is nothing unique nor exceptional in the chemical composition of the products in the Flourish line-up that warrants its use over more cost-effective competitors.

9. Fert dosing calculators

There are several fert dosing calculators available for EI and PPS-Pro. For both methods, I recommend rotalabutterfly.com as it contains an extensive list of chemical compounds and pre-mixed fertilisers (such as the Flourish range) for determining appropriate doses. Likewise, it lists teaspoon measurements for those who wish to dose ferts directly into the water column.
Note: As of writing, rotalabutterfly.com uses slightly higher nitrogen and phosphate concentrations for EI dosing at 7.5 and 1.3 ppm respectively. While a little higher than the lower threshold recommended doses I have provided, this is no cause for concern. Unfortunately the calculator does not allow aquarists to adjust ppm concentrations at this stage.

10. DIY dosing calculations

Some aquarists prefer taking out a calculator and using the oft-neglected ol’ noggin’ to calculate fert doses. The calculations are (relatively) simple, and it allows for targeting a specific ppm (which rotalabutterfly.com doesn’t yet support). The following three formulae are the most useful.

Formula 1: (x ppm) × (tank volume in L) × [1 ÷ [((number of nutrient atoms/molecules in compound) × (molar mass of nutrient)) ÷ (molar mass of compound)]]

This formula can be used to determine the mg of a dry chemical compound required to achieve x ppm of a particular nutrient.

Example: To determine the mg of KNO3 required to dose 8.5 ppm of NO3 in a 155 L tank, the calculation would be

8.5 × 155 × [1 ÷ [(1 × 62.0049) ÷ 101.1032]] = 2,148.28 mg of KNO3
Note: As an explanation, the formula arrives at the required dose of a compound by using the proportion of a nutrient's mass in a compound. It does so through molar masses, which is the mass of one mole (6.023 × 10^23 atoms/molecules) of a chemical substance.

Using the above example, the molar mass (i.e. the mass of 6.023 × 10^23 molecules) of KNO3 is 101.1032 g. Within 6.023 × 10^23 molecules of KNO3, there are 6.023 × 10^23 molecules of nitrate (NO3). This number of molecules is equivalent to one mole of NO3, and NO3's molar mass is 62.0049 g. Therefore, dividing 62.0049 by 101.1032 results in 0.61328. That is to say, 61.328% of any given mass of KNO3 will be in the form of NO3.

Following this, we can multiply the desired concentration of K (8.5 ppm) by the tank volume (155 L) to arrive at total mass of 1,317.5 mg of NO3. Given that 61.32% of the mass of KNO3 is NO3, we can therefore determine that 1,317.5 mg of NO3 is 61.32% of the target dose of KNO3. Following the formula, the target dose would be 1,317.5 × (1 ÷ 0.61328) = 2,148.28 mg.
The following drop-down infobox has a list of molar masses for common nutrients and fert compounds (and some other measurements):
1 gallon = 3.785 litres

Molar masses (grams)
Nitrogen (N) = 14.0067
Nitrate (NO3) = 62.0049
Phosphorus (P) = 30.974
Phosphate (PO4) = 97.971
Potassium (K) = 39.0983
Sulphate (SO4) = 101.1032
Potassium nitrate (KNO3) = 101.1032
Monopotassium phosphate (KH2PO4) = 136.086
Potassium sulphate (K2SO4) = 174.259
Formula 2: (x ppm) × (tank volume in L) × [1 ÷ % of nutrient]

This formula is a generalisation of Formula 1 and can be used to determine the mg/ml required of any iron chelate or any micro mix (whether dry or in a solution) or any macro solution in order to achieve x ppm of a particular nutrient. This is particularly useful for EDTA/DTPA iron chelates, as the iron composition varies from 6 to 12%.

Example: To determine the mg of a DTPA 9% iron chelate required to dose 0.35 ppm iron in a 120 L tank, the calculation would be

0.35 × 120 × [1 ÷ 0.09] = 466.66 mg of DTPA 9% iron chelate

Formula 3: [(volume of solution) ÷ (volume of dose)] × [Formula 1 or Formula 2]

This simple formula can be used to determine the mg of a dry fert (either an iron chelate or another compound) required for a DIY fert solution to achieve x ppm of a nutrient.

Example: To determine the mg of KH2PO4 required for a 500 ml solution where a 20 ml dose achieves 1.85 ppm PO4 for an 80 L tank, the calculation would be

[500 ÷ 20] × [1.85 × 80 × [1 ÷ [(1 × 97.971) ÷ 136.086]]] = 5,139.53 mg of KH2PO4.

11. DIY fert solutions

Many people with larger tanks often use approximate teaspoon measurements when dosing dry ferts directly into the water column (often referred to as dry dosing). However, when using smaller tanks (such as 5-10 gallon nanos), teaspoons may not offer ease of use in portioning out very small doses. In addition, dry dosing ferts in smaller tanks will sometimes require minute milligram measurements that most hobbyist milligram scales have difficulty in consistently weighing.

In many cases, people will often mix DIY solutions using pump bottles as this enables larger quantities of dry ferts that are easier weighed with a hobbyist milligram scale. Rotalabutterfly.com allows the calculation of fert quantities in order to create a solution for a given volume of water. Likewise, one can use Formula 3 in section 10.

It is recommended to use a slightly transparent bottle as this enables the examination of whether the fert has fully dissolved and/or whether there is mould growth. In addition, it is recommended to use either distilled or RO water as the solvent in order to limit the precipitation of the dry fert solute as a result of reacting with trace elements/compounds in tap water.

Is is normal for a micro fert mix in a solution to, over time, grow mould unless stored refrigerated or in a cool place out of direct light. Using dark, amber glass bottles can also inhibit the growth of mould. Some people create solutions to last for only 2-4 weeks to limit the accumulation of mould; others will create larger solutions and dose 10 ml of Flourish Excel (or a quantity of another preservative) per 500 ml of fert solution to minimise mould.

Some aquarists report mould growth in macro fert solutions, but this is most likely due to the use of tap water and/or inadequate sterilisation of bottles. It is recommended to use boiling distilled/RO water (it can be boiled using a microwave) to sterilise glass bottles. If using boiled tap water, thoroughly rinse the bottle with distilled/RO water afterwards to dissolve and remove any trace elements/compounds remaining from tap water.

While macros (KNO3, KH2PO4 and K2SO4) may be safely mixed to provide a single solution for dosing, it is not recommended to mix macro and micro ferts in a single solution given the high risk of precipitation between iron and phosphate (into ferrous phosphate) in concentrated solutions.

An additional aspect that is important to consider is the solubility of ferts. As an example, it isn't feasible to dissolve 100 mg of KNO3 in 100 ml of water for a highly concentrated fert solution. When water is at room temperature (20 degrees Celsius, 68 degrees Fahrenheit), the solubility of KNO3 is 20.9 grams per 100 ml, and the solubility of KH2PO4 is 23 grams per 100 ml.

The solubility of micro ferts varies from chelate to chelate, and unfortunately there is little information about the solubility of Plantex CSM+B. Howver, as an example, a DTPA iron (11.6%) chelate from Rexolin has a solubility of 11 g per 100 ml at 20 degrees Celsius.

While you can use a hot water bath or use boiling distilled/RO water to increase the dissolution of the fert solute, there is a tendency for the fert to precipitate out of the solution as the temperature decreases and adjusts to the ambient surroundings. In most cases, it's recommended to use between 50-80% of a fert's solubility in mixing DIY solutions.

12. Carbon intermediaries

Excel and Metricide 14 are commonly used as a carbon supplement in low tech tanks where additional CO2 is not injected. Glutaraldehyde, the active ingredient in both products, is not a same-for-same equivalent for CO2: it instead offers carbon intermediaries which plants can take up as a source of carbon.

In addition, glutaraldehyde has latent algaecidal effects at normal doses (some aquatic plants, such as Vallisneria spp. are also sensitive) and in sufficiently high concentrations, it can function as a pesticide and herbicide. Because of this, it is normally not recommended to overdose either product in order to supply an excess of carbon intermediaries for plant uptake.

The equivalence of glutaraldehyde in terms of CO2 ppm is difficult to establish. Anecdotal reports suggest that it is, at most, 40-60% effective as CO2 and is equivalent to 5-10 CO2 ppm. In any case, the use of Excel or Metricide 14 should not be used with the understanding that it is a perfect substitute, and it should not be overdosed under the assumption that "more is better".

Aquarists report different EI dosing adjustments when using Excel or Metricide 14 in low tech tanks. Typically most people maintain 50% or 100% of the recommended dose once per week.

13. Substrates and substrate fertilisation

One will notice that all the aforementioned fert dosing methods rely on adding nutrients directly to the water column (often called water column dosing). The general consensus is that most (if not all) aquatic plants do not seem to display a preference for nutrient uptake either through the substrate (via subterranean roots) or through the water column (via leaves, stems and aerial roots). Plants will essentially seek nutrients wherever they might occur. Because of this, it is perfectly possible to achieve excellent, robust growth by only dosing the water column.

The use of substrate fertilisation (e.g. root tabs, worm castings, etc.) is quite widespread, although its relationship with water column dosing is a bit contested. Some insist that plants which are claimed to be heavy root feeders (e.g. Cryptocoryone spp.) will require root tabs. Others suggest that it isn’t necessary given the capacity of plants to take up nutrients through the water column. Some practice substrate fertilisation in order to lessen the quantities and frequencies of ferts dosed into the water column.

In most cases, the use of substrate fertilisation should be seen as an optional and beneficial supplement to water column dosing. For example, many would suggest the use of root tabs in areas of the tank where water circulation is poor due to high plant density and/or hardscape features.

The role and selection of substrates in providing ferts for plants is a complex topic and will only be lightly treated here in this guide. Like substrate fertilisation, the relationship between substrate choice and fert dosing is somewhat complicated. Some view nutrient rich substrates (like Aquasoil or a potting soil mix) as necessity to ensure good plant growth, while others report excellent growth using an inert substrate (such as Eco-Complete gravel or sand). There is a tendency that nutrient lean methods of water column dosing (PPS-Pro, ADA) are matched with nutrient rich substrates. Likewise, EI - on account of its nutrient rich water column dosing - can offset the lack of nutrients in inert substrates.

One substrate quality that is often discussed is Cation Exchange Capacity (CEC), the capacity of substrates to bind dissolved nutrient ions in the water columnswithin itself and closer to the root structure of plants. High CEC is generally understood as a benefit, with soil substrates (such as Aquasoil) possessing a high CEC, while gravel substrates (such as Eco-Complete) having no CEC. That being said, there are overwhelming reports of planted tank aquarists successfully growing most (if not all) species well in low nutrient, low CEC substrates with water column dosing.

The choice of substrate, then, should be seen in relation to both its advantages and disadvantages. A substrate such as Aquasoil is nutrient rich and possesses a high CEC, but most nutrients are typically exhausted in 8-12 months and the fired clay pellets tend to unbind into a slurry over the course of 2-3 years. In comparison, an inert, zero CEC substrate such as Eco-Complete will essentially endure for all time, and can develop CEC over time with an accumulation of mulm (tank detritus, such as solid fish waste, decayed plant matter and decomposed excess fish food). However, these gravel-based substrates can be difficult to plant in as the low density of gravel typically has little compacting strength around underdeveloped root structures.

14. Example of fert dosing regimens

Here are some typical aquariums with an example of their fert dosing regimen under EI and PPS-Pro.

Low tech (low light, no CO2) 5 gallon nano with Excel, pH of 7.5:

Monday: 154.67 mg KNO3 and 137.22 mg KH2PO4
Tuesday: 58 mg Plantex CSM+B and 34 mg DTPA iron (11%) chelate
Sunday: 25% water change

To be updated.

Low tech (low light, no CO2) 20 gallon tank with Excel, pH of 6.5:

Monday: 618.68 mg KNO3 and 548.88 mg KH2PO4
Tuesday: 464 mg Plantex CSM+B
Every second Sunday: 50% water change

Note: Plantex CSM+B has been safely doubled over recommended dose. This is because at 6.5 pH, only 50% of CSM+B's EDTA iron chelate is biologically available for plant uptake.

To be updated.

High tech (high light, 30 ppm CO2) 40 gallon tank, pH of 6.5 during CO2, pH of 7.8 during rest period:

Monday, Wednesday, Friday: 1,237.36 mg KNO3 and 1097.67 mg KH2PO4
Tuesday, Thursday, Saturday: 9.5 ml Flourish and 275 mg DTPA iron (11%) chelate
Sunday: 50% water change.

To be updated.

  • #3
This should be stickied!
  • #4
Yep this would make a good sticky. I'll be referring to this for my new 7 gallon build
  • #5
Well written.
  • #6
What a fantastic summary! I recognize a number of the principles you’ve included, but you’ve done a great job of synthesizing a ton of info in one place.
I absolutely agree this should be stickied!!
If I could offer one suggestion, include a table of contents or index at the top, with each item linked to the relevant text below (I don’t even know if that latter can be done on this platform).

  • #7
Stickied. Thanks for taking the time to write this!
  • #8
Much needed, dry ferts and iron especially. Thanks for linking my post! I'm writing a general planted tank guide and I'll link this in the nutrients section, I couldn't write anything better myself. Looking forward to the addition of PPS-Pro
  • #9
Great article! I think you should add a little note on the EI method that says something along the lines of, excess nutrients DO NOT cause algae. Instead, fluctuating water parameters, improper lighting or CO2 are the cause of algae. Unlimited fertilizers do not cause algae. I think this is a common mistake thought by beginners, that excess nutrients cause algae, when really, as Tom Barr and others have proved multiple times, excess nutrients will not cause algae. However, I have found if you get your fert ratio out of balance, e.g. too much of KH2PO4 and a deficiency of KNO3, you can quickly develop algae problems.

We needed something like this, great job. Can't wait to see it as it develops and has more added to it.
Inactive User
  • Thread Starter
  • #10
Thanks everyone! I based the thread off a personal document to which I had, over several weeks, been adding weblinks, guides, molar masses, chemical analyses and other planted tank matters as a sort of reference point for my own tank.

I thought that it was a good idea to organise it and make it available for other planted tank aquarists. Dosing ferts is, on principle, fairly simple with a gentle learning curve: but there's a lot of areas where you can make small (and often frustrating mistakes). Hopefully this thread will make it a simpler process for other beginners!

If I could offer one suggestion, include a table of contents or index at the top, with each item linked to the relevant text below (I don’t even know if that latter can be done on this platform).

Thanks for the suggestion, and added! I had a look around, but it doesn't look like this platform supports the [anchor][/anchor] and [go to=][/goto] tags for BBCode. I agree that it would've been useful due to the length of the thread.

Much needed, dry ferts and iron especially. Thanks for linking my post! I'm writing a general planted tank guide and I'll link this in the nutrients section, I couldn't write anything better myself. Looking forward to the addition of PPS-Pro

You're welcome Mak: your posts have definitely been a wealth of information for me.

Great article! I think you should add a little note on the EI method that says something along the lines of, excess nutrients DO NOT cause algae. Instead, fluctuating water parameters, improper lighting or CO2 are the cause of algae. Unlimited fertilizers do not cause algae. I think this is a common mistake thought by beginners, that excess nutrients cause algae, when really, as Tom Barr and others have proved multiple times, excess nutrients will not cause algae. However, I have found if you get your fert ratio out of balance, e.g. too much of KH2PO4 and a deficiency of KNO3, you can quickly develop algae problems.

We needed something like this, great job. Can't wait to see it as it develops and has more added to it.

Thanks for the suggestion, and added! Definitely an important thing to keep in mind since so many aquarists tend to rush to "excess phosphates" when trying to deal with algae in their planted tanks.

A few updates: added section 10 DIY dosing calculations, section 13 substrates and substrate fertilisation, a few other changes here and there.

Many thanks jdhef and Mike for helping to rescape the thread a bit as I had initially reached the 20,000 character limit on the first post!

  • #11
10. DIY dosing calculations
... The calculations are simple ...
Formula 1: [((x) ppm) × (tank volume in L)] × [1 ÷ [((number of nutrient atoms/molecules in compound) × (molar mass of nutrient)) ÷ (molar mass of compound)]]
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  • #12

You're right: it definitely needs some fixin' I think. Partially, I suppose it's the cumbersome way in which I've written it. The website doesn't support equation formatting, and even if it did, I was afraid that the use of abbreviations (like M = molar mass) might just confuse people.

I've edited the formula, but I think I might just add an explanation of what it is exactly that the formula does.
  • #13
Deemed scholastically unsuited in the third grade, I have to use what is available.
  • The free solar powered electronic calculator that AARP gave me for joining years ago.
  • Volume metric conversions off a whiskey bottle.
  • Mass metric conversions off a bag of flour.
  • Passing familiarity with grammar school arithmetic.
That's all I needed so far.

Still, I applaud your effort even if I'm too stupid to use it.
  • #14
Deemed scholastically unsuited in the third grade, I have to use what is available.
  • The free solar powered electronic calculator that AARP gave me for joining years ago.
  • Volume metric conversions off a whiskey bottle.
  • Mass metric conversions off a bag of flour.
  • Passing familiarity with grammar school arithmetic.
That's all I needed so far.

Still, I applaud your effort even if I'm too stupid to use it.
Hope you were paying attention, rumor has it there's going to be a pop quiz. Us olds are doomed.

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