Is it true? pH tests don't work when the alkalinity is close to zero

Hello,

I have a 15G moderately planted tank and I recently added a nerite snail in there. Since the tank has been running smoothly without any issues for a couple of years now I never worried about water hardness etc. I've always used a pH pen to read the pH and it was always between 7.2-7.8. Since adding the snail I wanted to test if there's enough Calcium for the snail and accurately measure the pH. So I bought some API test strips and API liquid KH/GH tests.
My water supplier provides a very detailed analysis of the water, updated every month, which gives minimum/maximum/average values for pretty much everything you can imagine BUT KH.

So here are some values:
Water supplier (Birmingham, UK):
pH: 7.10 min, 7.73 average, 8.22 max
GH: 2.64 degrees
KH: N/A

Tap:
pH: 7.6 (using pH pen), API strip no reading! No change of colour at all.
KH: 0 (using test strip), 0-1 dKH (one drop only) from API liquid KH test
GH: around 3dGH using both strips and liquid GH test (3 drops)

Aquarium water:
pH: 7.6 (using pH pen), API strip no reading! No change of colour at all suggesting a pH lower than 6!
KH: 0 (using test strip), 0-1 dKH (one drop only from API liquid test)
GH: 10dGH using API strip, 10 using liquid test. (explained due to adding an edible calcium block for the snail)

I found an article from a reputable website here in the UK stating that pH tests fail to give accurate readings when alkalinity is close to zero (as pH tests are like microphones, pH is like "noise", and KH "amplifies" the noise. So low KH = inaccurate reading of pH)



I haven't had any issues with my tank but I'm wondering if I can even trust the pH values of any test with such low alkalinity. My pH meter broke (urghhh) and the API test strips don't work. I understand that there might be a possibility that my tank water pH is low in the tank and the api test strip is accurate (Which is scary as the pH is too low for my snail - my fish would probably like it gbr, cardinals, cories, otos). BUT what makes me not trust the api test is the fact that the pH pen even if it's cheap did give a realistic reading, and also the fact that the strips fail to measure the pH of the tap water which according to the supplier is slightly alkaline.

Have you ever had any similar experience with 0KH and pH tests?
Can anyone try testing the pH of distilled water (KH should be zero and pH 7)?
How can the pH be acidic when the GH is close to 10?
Is it possible to have 0KH and 10GH?
Would crushed coral even work to increase KH when the pH is above 7.5?

I ordered a seachem pH alert and some crushed coral (i'm intending to add just a tiny amount so that my KH is about 3).

 

I have very similar water as you, and I have learned how to treat it for the fish.

When the water comes from the tap with very low KH (KH=0), then the pH is actually unstable.

pH is the concentration of positive Hydrogen ions relative to the total positive and negative ions. So it's a ratio.

But when there are no buffers (KH=0) then the total number of ions is very low. So pH is a ratio with a small number in the denominator. If you add just a little Hydrogen pH would jump up!! But really nothing has changed since the change is small.

So pH doesn't make sense when the water has no buffers. What that means is that you can't really measure the unstable pH with low KH water. But at the same time, it means that wild swings in pH really don't indicate any major change either.

Let the tap water sit out overnight though. It will absorb some KH from the air (from carbon dioxide). This will stabilize the pH and the various tests will all measure the same thing. This is what your water company means when they say that the water is pH=7.7. That is the typical value you get for low KH water that sits and equalizes to the air. But it must sit first. You can't measure the pH of water straight from the tap.

The real problem for aquariums is that the biofilter requires KH to function. So the cycle can stop if you have no KH.

But, a little bit of KH comes from the C02 in the air, so if you have a very light load, the tank can cycle with KH=0.

But if you add enough fish so that the rate of C02 absorption is not enough to sustain the cycle, then the tank will crash. That means ammonia goes up.

This is why we say that the KH should be around 5 degrees minimum. This keeps enough buffer in the water to maintain the cycle. It also makes the pH stable.

So I add buffers to my water (I actually have a whole house soda ash treatment system) to set the pH=7 and KH=8. My fish are all happy! The treatment system keeps the water from being corrosive in the pipes so that the copper does not leach out. I monitor and copper levels are 0.

Other folks add some crushed coral to the rocks (say 1 pound per 10 gallons of water).

 

Thank you for your answer Frank.
I'm actually adding CO2 to the tank by means of passive CO2. Wouldn't that help increase the KH? The tank is fairly well established and has quite a few plants including some floating plants which are known to consume nitrates. From the tap nitrates are 4.1. Before I relocated 2 years ago my tap water had 40ppm nitrates out of the tap so I added seachem denitrate media in my filter... and it's still in the filter. So my nitrates are always 0-10ppm. The test strips measure 0 for both? Does 0 KH affect existing bacteria or slows down their reproduction?

I have ordered some crushed coral and I'll update if there's a change in the water parameters?

All my fish are and have been healthy. Am I worried over nothing?

 

For sure, if your tank is healthy then you are worried about something that is not important! But we all try to understand what is going on with our tanks. Plus you may want to branch out to different style tanks that work differently.

But apparently for your tank, the C02 from the air (and your injector) is adding enough carbonates to keep the cycle going for the bio-load that you have.

All tanks achieve a balance, but balance in a different place.

The biofilter actually consumes carbonates in order to convert ammonia. So there must be a constant supply of carbonates.

In many of my tanks, with the amount of fish I have, there is not enough carbonates from the air to sustain a cycle. So I buffer the water with carbonates, and it is stable. The carbonates never get exhausted, and then I change the water which adds more. So I am in balance.

You are too, just at a low place. Your tank is precarious though. If the bioload were to increase, then the BB colony would grow and perhaps start to use carbonates (KH) at faster rate then you are replenishing. Then it might crash.

I also sometimes have a dead fish, or some kid adds a lot of food. So I like to keep the KH up around 8 to absorb those spikes. With a low KH, you can't absorb spikes.

 

Page 3, Option Two.

https://assets.fishersci.com/TFS-Assets/LSG/Application-Notes/AN-PHPURE-E-0914-RevA-WEB.pdf

 

Every living cell, whether in plants, animals or microorganisms is surrounded by a cell wall. That cell wall acts as a gatekeeper to control the flow of water, salts, nutrients, and waste products between the inside of the cell and the outside. This process is called osmoregulation. The cells and the organism to which they belong will function best when there is stability in the concentration of various chemical compounds both inside and outside the cell wall. With fish and aquatic plants, changes in the concentration of various chemical compounds within the water in which they live will cause an upset in the osmotic balance of compounds within the cells as well. Thus, fish and plants do best when water parameters are stable.

If you look at the water parameters provided by your local water company, you will see that the concentration of minerals is rather low. That means that even slight changes in mineral content will represent a large percentage change in concentration. This is most obvious in the case of alkalinity or KH. Although we often call KH carbonate hardness, it is really a measure of the ability of the water to buffer changes in pH due to a variety of anions in the water, including carbonates, bicarbonates, phosphates, borates, etc. In seawater, the concentration of these anions is quite high, so the pH of seawater is highly stable. In your water, there are few of these anions to buffer pH changes, so the pH can vary from 7.2 to 8.2. Since pH is measured on a logarithmic scale, that represents a concentration change of hydrogen and hydroxyl ions of more than a factor of 10. Thus, the change is more than 1000%. The buffering capacity of the water is so low that even changes in the dissolved CO2 will cause significant pH swings. Since you have passive CO2 addition, you will never get an accurate measurement of pH. If you had a pressurized CO2 system on a timer, the pH would really swing between day and night.

If the pH in you aquarium is changing, the cells of your fish and plants will have to change to stay in equilibrium with the water. That is stressful to both plants and animal . Thus, it is good to add anions to your aquarium water so that changes in pH will be buffered and the water parameters will remain stable.

In freshwater aquariums, the common anionic buffers used are either based on carbonates, bicarbonates, or various forms of phosphates. In saltwater aquariums, carbonate and borate buffers are often used. I do not know what brands of buffers are available in the UK. Here in the States, API offers a Proper pH 7.0 buffer and a Proper pH 7.5 buffer for freshwater aquariums. These are phosphate based buffers that work well. However, some aquarists with planted tanks try to minimize addition of phosphates to control algae growth. Seachem offers an Acid Buffer and an Alkaline Buffer that do not contain phosphates, but you have to add specific amounts of each buffer in a prescribed ratio to target a specific pH.

At the very minimum, you want the dKH in your tank to be at least as high as your 3 dGH hardness, but bringing it up to 8 dKH would be even better.

Crushed coral is primarily aragonite which is comprised of calcium and magnesium carbonates. As it dissolves slowly in your water, it will increase both GH and KH. Some fish like soft water, some like hard water. Thus, whether you choose to use crushed coral or buffers depends upon the water hardness you wish to achieve. You nerite snails comes from brackish water where the water is pretty hard and the pH is on the higher side, so it would appreciate the crushed coral, but you did not state the types of fish you are keeping, so I do not know the pH and hardness levels that might be most appropriate.

 

Crushed coral is primarily aragonite which is comprised of calcium and magnesium carbonates. As it dissolves slowly in your water, it will increase both GH and KH. Some fish like soft water, some like hard water. Thus, whether you choose to use crushed coral or buffers depends upon the water hardness you wish to achieve. You nerite snails comes from brackish water where the water is pretty hard and the pH is on the higher side, so it would appreciate the crushed coral, but you did not state the types of fish you are keeping, so I do not know the pH and hardness levels that might be most appropriate.

Thank you for your input, Ray. Very informative. If anything it made me understand how important KH is. I did briefly mention the fish I keep in the first post. I keep a German blue ram, cardinal tetras, cories and otos (And one nerite snail). So I think my fish love the low hardness/acidic conditions, but as u said stable parameters are key. I'm waiting for the crush coral to arrive and I'll keep an eye on the kh/gh values. If i stop feeding the snail mineral blocks I hope to have kh and gh around 3 and 6 respectively.

In the UK we have both API and Seachem buffers, but i'm a bit reluctant to go down that route as I don't know how easy it is to mess up. My thinking is that once the crushed coral increases the KH of the tank hopefully water changes won't be as stressful. If i trust the water company, the water should be slightly alkaline (same as my tank after crushed coral) and minerals will be released on demand when the pH drops.

Would you say that the api strip test suggesting a ph of max 6.5 is correct? or the alkalinity is too low to get a reliable reading from it?

Just trying to have an answer to the topic title for people who are interested.

 

Would you say that the api strip test suggesting a ph of max 6.5 is correct? or the alkalinity is too low to get a reliable reading from it?

Just trying to have an answer to the topic title for people who are interested.

If you are using the API KH test, it uses bromthymol blue as the indicator. Bromthymol Blue is blue at alkaline pH, green at a neutral pH and then yellow at acid pH. The API indicator solution contains the dye and a dilute solution of acid. As you add one drop at a time, the acid consumes any residual alkalinity until there is none left. Then the next drop will change the color to yellow, indicating the pH is now around 6.0 in the test vial. .

The API test strip uses a variety of indicator dyes that change color at various pH levels. Thus, the pH you measure may well be accurate at the moment of testing, but with a low KH, the pH can be unstable. If the pH really is 6.5, a single drop of the acidic KH test reagent could easily drop the pH level to 6.0 or below.

Some species like Blue Rams and Cardinal Tetras do well in soft, acidic water. However, snails do not do well under those conditions as their shells are comprised of calcium carbonate and they will disolve in soft, acidic water.

 

Ray, you are a star! thank you.
Do you have any idea how the digital pH pens work? Are they more reliable than dye tests?

 

Ray, you are a star! thank you.
Do you have any idea how the digital pH pens work? Are they more reliable than dye tests?

A pH meter contains a specialized glass probe that contains a silver/silver chloride electrode. The voltage across the probe is related to the hydrogen ion concentration in solution (pH). The electronics in the meter simply measure the voltage and convert it to pH units. If a pH probe is cleaned properly and calibrated properly, the meter can be accurate to 0.01 pH units. That if far better than the accuracy of the colormetric methods. However, if the probe gets fouled or the meter has not been calibrated properly, then it can be highly inaccurate. In a laboratory where accuracy is critical, the probe will be calibrated frequently. Fishkeepers tend to be far more lax about such matters. That is why, even though you have a pH meter (in this case a self contained pH pen), it is always good to do colormetric testing periodically to make sure the calibration is not off significantly.

I use a Milwaukee pH meter in my primary tank and use an inexpensive pH pen to check other tanks. However, I use the API pH tests to check pH in each tank on a weekly basis to make sure the calibration of the meters has not drifted. If there is a discrepancy, I use buffer solutions to recalibrate the meters.

 

A pH meter contains a specialized glass probe that contains a silver/silver chloride electrode. The voltage across the probe is related to the hydrogen ion concentration in solution (pH). The electronics in the meter simply measure the voltage and convert it to pH units. If a pH probe is cleaned properly and calibrated properly, the meter can be accurate to 0.01 pH units. That if far better than the accuracy of the colormetric methods. However, if the probe gets fouled or the meter has not been calibrated properly, then it can be highly inaccurate. In a laboratory where accuracy is critical, the probe will be calibrated frequently. Fishkeepers tend to be far more lax about such matters. That is why, even though you have a pH meter (in this case a self contained pH pen), it is always good to do colormetric testing periodically to make sure the calibration is not off significantly.

I use a Milwaukee pH meter in my primary tank and use an inexpensive pH pen to check other tanks. However, I use the API pH tests to check pH in each tank on a weekly basis to make sure the calibration of the meters has not drifted. If there is a discrepancy, I use buffer solutions to recalibrate the meters.

Thank you ever so much for the valuable info. I will update this thread when I receive the crushed coral in a couple of days.

 

Update: I got a new digital pH meter and calibrated it using buffer solutions.
The pH in the morning before lights turned on was 6.2! I have added two teaspoons of crushed coral in a mesh bag and added it to my filter. The following morning the pH reads 6.5. KH is still 0-1 but I suppose it will start building up once the pH becomes more neutral.