gauging CO2 levels in tank

[deeloke]

Hi. I am quite new to fish tank water management. So i am sharing some advise on water testers offered by an engineer at JBL who manufacture the JBL "EasyTest 5 in 1" Test strip. I wrote to them asking why their test kit displays a PH value of 6.4, when my Tetra PH test (test tube + solution) produces a result of 7.

I was hoping to use the test strip results to determine the CO2 level via
the formula =3*KH*(10^(7-PH)). However the results were crazy (CO2 of 72) but my fish are very healthy and are not showing any signs of CO2 poisoning, which I would expect with a CO2 of 72! To compound this, my plants are not producing oxygen bubbles, nor are they thriving, which again suggests the CO2 is not so high. The temperature of my tank is 26.7 degrees celsius.

Anyway, the JBL engineer shared this with me:
"Test strip are compound to check the water parameter quickly. So they cannot have the demand of pinpoint accuracy. So it is possible, that by reading the scales accure inaccuracy, especially by NO2 and pH.

For calculation of CO2 level in water you have to scale the KH with an drip test with the doubled water (so you can find the KH on 0,5 degrees) and pH ideally verify electronically with an Electrode.

The simple calculation of CO2 level in water results in wrong conclusion."

Hope this helps others out there getting into planted tanks and CO2 control.
I am still looking for an economical way to test CO2 as i have added a CO2 reactor to my 32 litre tank and I am worried about the health of my fish.

[gemo82]

Thanks for sharing this helpful information for those who intend to be more precise about water parameters. Let me add the point that even if you can measure the pH accurately, it will not give you an accurate CO2 level just by one simple formula. It works only if CO2 is the only factor that affects pH, so any decrease of pH can be related to the increase of CO2 level. This is not the case however, as there are other things present in the water to affect the pH. Peharps it is possible to calculate based on the initial pH, compared to the pH after adding CO2, but it will be another formula all together.

Most hobbiest rely on visual signals to gauge if CO2 level is too high, like fishes at water surface etc, and using a not-so-accurate but economical drop checker to gauge if CO2 is in the "safe-zone". No need to be precise, but it serves its purpose. Do a search on drop checker to know more.

[Fuzzy]

Generally the multi-test kits are not as accurate as the stand alone tests. I am using mostly API test kits, they are fast, accurate and relatively inexpensive.

I still have some leftover Tetra kits that I am using up but I find those to not be as accurate as the API, they are about a year older though.