Measuring CO2 concentration

[wks]

Hi, I would like to know the concentration of CO2 (ppm) being diffused into my 3 ft planted tank but I'm using ADA Aquasoil which can affect pH . Has anyone here found an alternative way to measure CO2?

[FC]

What is your tank's water volume?

For estimative method, for every 100 litres of water, inject about 1.2 bubbles per second. For this method, you have to turn on/off the CO2 (solenoid) with the light and applies to tank up to 600 litres.

It will not be easy to accurately measure CO2 under your tank's water condition, I think. You have to do it with the estimative method and at the same time observe the plants' and fishes' reactions.

[PeterGwee]

ADA aquasoil tends to drop both pH,KH and GH down to pretty low levels during the initial first few weeks or months depending on the amount of water change done by folks. The problem here is the pH/KH/CO2 relationship breaks down when KH is less than 1 and whenever that the buffer is not a carbonate buffer. You can try to overcome the issue and get a close estimate of where your CO2 is by the following methods:

1)Try to get some coral chips and place it in your filter to counter the effect of the peat from aquasoil.

2)Whenever you want to determine the current CO2 level, take a sample of the tank water and measure the KH first. If less than 1 or so, you would need more coral chips or add baking soda to get it to 3 or so. If the KH is 3 or higher, aerate the tank water sample for 24hrs or so. Take readings at particular intervals to find out if the pH has hit the highest possible level. (Ambient CO2 level).

3)Determine the pH/KH of the aerated sample. Find the amount of ambient CO2 using the pH/KH/CO2 chart. If your ambient CO2 level is showing more than 4 or so, don't trust it. Substract the amount found by 2-3ppm. That is the amount of error. Eg. Measure and found 12ppm of ambient CO2 from the chart..Substract 12ppm by 2ppm hence an error of 10ppm for the amount of CO2. Inject CO2 to the by to get a CO2 level of 40ppm would give you an actual estimated CO2 level of only 30ppm. (Do note that this would only work if the KH of the aerated sample and the tank is still the same after 24 hrs or so.)

Another point to take note is the GH..nothing to do with the CO2 though but plants need calcium and magnesium as food as well which is why you would need to supplement it if your GH is less than 3 and hopefully still pretty balance in concentration. Best at 3:1 but singapore's tap is fine at 5:1 (Ca:Mg).

A personal point of view is that why did you use aquasoil when you wish to determine the proper CO2 levels? I used it once and dump it after I find it a PITA for determing the correct CO2 level. Oh, the tonina and some taiwan plants wasted away during the period as well hence the thought of tonina growing great in aquasoil is still a myth. Some ground peat is fine at the very bottom of a new substrate helps to jumpstart the tank for organic stuff but mulm from an old tank is more important than the peat. Plants need light, CO2 and nutrients (each plants need different amount of nutrients but a good range would keep them all happy). If it ain't the mention 3 stuff, it won't grow plants.

Regards
Peter Gwee :wink:

[wks]

Thanks Freddy and Peter for your reply, my original intention of using ADA Aquasoil is to throw it away after 3 years (lfs people also said it will turn into mud by then), about the time to move my house. I hate to wash the gravel again when I'm going to set up a new tank, just plain laziness. :wink:
My reason for wanting to find out the CO2 concentration is to determine the cause of slow or stunted growth of the plants.

Regards
Jason Wong

[hwchoy]

my experience with Aquasoil so far hasn't been good. I am replanting a tank with Aquasoil topped with Lonestar (to hold the plants down), just crypts with CO2 injection. Let's see if they'll do better this time.