The science of CO2 calculation.

[nurburgring]

I have read that CO2 is being determined by

1) Your kH reading
2) together with the acidity of the water

A certain kH together with a certain PH level points to the amount of co2 you have, right ?


However, I was thinking , must you take the current PH level of your water into consideration ? What if the water I have is initially already acidic or alkaline ? FOr example what if I have crushed corals in my tank that drives PH up to 8 without CO2 injection, and then I give it a massive 10 bubbles per second to drop it down to 5.5 PH ?

I'm sorry, still learning the basics. I currently have a sera "in the tank" CO2 tester which tells you immediately how much CO2 is there in the tank by reading off the colour. I find it always gives me a similar reading ; too much co2. Is that reliable ?

Doesnt help I failed chemistry class. :duh:

 

[Rex Grigg]

The pH/kH/CO2 chart is based on a two things.

1. The only buffers in the tank are bicarbonates.

2. The only thing used to lower pH is CO2.

Now, wood or peat can/will lower the pH skewing the chart. Adding many pH additives will do the same.

If all you used was crushed coral the chart would still be valid.

 

[loaches r cool]

Yeah, often times the chart isnt going to work well for our aquariums. Even if we didnt have anything else effecting the water you would still need test kits more accurate than what most of us use. For example, the units on my ph test are .2 already, and often times its hard to tell exactly which one it is, so your margin of error is probably greater than .2. Most KH test kits are in 1 degree increments as well. Your error could really double or half your co2 calculation. Of course if you happen to use high end test kits then it'll be much more accurate. Probably the most accurate method I hear talked about often is the DIY drop checker, take a look here: http://www.aquaticplantcentral.com/forumapc/do-it-yourself/32100-diy-drop-checker.html

 

[Squawkbert]

Or - take a baseline pH reading w/o any added CO2 in the water (leave it off for a day), then crank up the CO2 for a day and take another pH reading (needs to be same time of day as plant respiration/photosynthesis will alter your CO2 as a function of the time of day). Now you have 2 readings. The one w/ CO2 running should be a little lower. That drop in pH, along w/ knowing your Kh should allow you to compute your CO2 system's contribution to the total CO2 level. (personally, I use a drop checker and have contributed to related threads in APC, AA and here).