Regarding General Hardness (GH) in a planted aquarium with tropical fish


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Can someone check my logic here?

PH = Percent Hydrogen
GH = General Hardness (measured in dH)
KH = Irrelevant
dGH = Degrees General Hardness
dH = Degrees Hardness
TDS = Total Dissolved Solids
PPM = Parts Per Million

33 Gallon Aquarium Information
Current PH: 6.2-6.4
Target PH in the future: 7ish
Current GH: near 0
Current KH: near 0
Target GH after this water change: 1dGH
Future Ultimate final/target GH: 6-8dGH

Seachem Equilibrium, my GH increaser, says to use 16g or 1 tablespoon for every 20 gallons to raise the GH by 3dH.

"To raise mineral content/general hardness (GH) by 1meq/L (3dH), add 16g (1 tablespoon) for every 80 L (20 gallons) when setting up an aquarium or when making water changes (add to new water)."
-Word for word instructions from the label

I have a 33 gallon tank, so if we cross multiply and divide to get a proportionate ratio I come up with a total requirement of 26.4g of Seachem Equilibrium to raise my 33 gallon tank by 3dH.

16g = 26.4g
[HR][/HR] 20gal = 33gal

(16x33) % 20 = 26.4

I only want an increase of 1dH, so I divide 26.4g by 3 to get 8.8g. That means 8.8g of Seachem Equilibrium raises my dH by 1 for a 33 gallon tank.


1) It doesn't matter how much water I add the Seachem Equilibrium into? All I consider is the ultimate tank size, 33 gallons.

2) Considering these fish have never had any hardness in there water, is increasing the GH by 1dH per day too severe? Should I raise it by 1dH every other day? Should I raise it by .5dH?

3) Is it true that dGH can be found with a TDS meter by utilizing the following formula:
PPM = dGH * 17.9
dGH = PPM % 17.9

And if so wouldn't that make my GH kit useless, as I have a TDS pen?

4) I have the following fish and lots of plants. Based on the following table I think an ultimate dGH of 6-8 would be ideal. Or does that not matter as much? As long as its close?
Lemon Tetra
Pristella Tetra
"White Cloud" Mountain Minnows
Zebra Danios
Blue Neon Tetra
KuhlI Loaches
Corydoras JuliI Catfish
Zebra Horned Nerite Snails
Amano Shrimp

0 - 4 dGH 0 - 70 ppm very soft
4 - 8 dGH 70 - 140 ppm soft
8 - 12 dGH 140 - 210 ppm medium hard
12 - 18 dGH 210 - 320 ppm fairly hard
18 - 30 dGH 320 - 530 ppm hard
over 30 dGH over 530 ppm very hard

Thank you for any information.


Well Known
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5 to 10 years
1. Correct. The problem'll have a hard time trying to dissolve 8.8 grams of Equilibrium in a small volume of water (like a gallon or less)
2.Yes. An increase of 1 dGH in a day is not necessary and could be too severe for sensitive fish.
3. No. All your GH reading will be "included" in a TDS meter reading but the other way around is not true. As far as I know, ApI GH drops test uses EDTA to bind divalent cations only: calcium, magnesium, iron, manganese...Any substance that ionize in water will show on a TDS meter (anions and cations) but only divalent cations will show on GH. As an example:
Sodium chloride solution shows high on TDS and zero on GH or KH
Baking soda shows high on TDS meter, zero GH, high KH
Calcium carbonate shows high on TDS, high GH high KH
Organics (sugars, proteins) : zero on TDS, GH or KH and still, they are good contributors in fish osmoregulation


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San Diego CA
1 year
Let's start at the top:


pH =/= percent hydrogen
pH = potential of hydrogen. lower pH actually means more hydronium ions in your water = more hydrogen = more acidic

GH is general hardness... but does not measure everything in your tank (as the above poster explained).

KH is NOT irrelevant to the aquarium hobby. KH keeps the pH constant. The nitrogen cycle is an acidic process and KH measures the amount of carbonate in your water. carbonate reacts with the acids produced by the nitrogen cycle. Without a sufficient KH, your acids will build up and eventually crash your pH downwards.

the rest of the definitions are fine, as long as you know what they are measuring. KH measures carbonates, GH measures divalent cations, TDS measure everything dissolved in your water, including carbonates and divalent cations.


to your questions:

1. As long as you can dissolve it, it will be fine.

2. Increase as you wish, just know that too slow can be bad. These are chemicals that the fish need for osmoregulation, etc.

3. No. See above poster's answer. As an example, my tap water is a KH of 8, GH of 14. even if you add these together for 22 * 17.9 = 394. But my TDS is 485, so there's another 90 ppm of SOMETHING in the water not accounted for by the two tests. Additionally, even if they WERE the same, more information and double checks are never useless. It's called redundancy, and that's a good thing.

4. I'm not sure as for desired levels. But don't forget about KH being important as well.

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