24hr Co2 Test

[xing]

I've just done a ph test of my water to try and work out the co2 level based on ph of tank water and ph of water removed 24hours earlier. I understand that 1 ph difference of 1 indicates apporx 30ppm.

However my tests are showing both sample the same at 6.8 even though I'm adding co2 through a diy yeast bottle setup (soon to become pressurised). Full stats are

ph 6.8
kh 0 (which would indicate nil co2 i think)
gh >6d
NO2 nil
NO3 50ppm

how can I have nil (or near as damn it ) co2 when adding through diffuser at a rate of 4-5 bubbles per second into 65usg (approx). When I go pressurised will this improve (can't see how) or will i need higher bubble rate.

Or are my test kits so unreliable as to be useless??

Any help please

 

[Themuleous]

I think the anomaly here might be the KH. Getting a Co2 measurement from KH/pH can only work if there is KH to measure. How about trying the drop checker method? Or alternatively up the KH manually with bicarb and redoing the pH test then. You only need to be able to measure the KH so 1KH would be enough. It wont affect the fish

Sam

 

[xing]

so could i take a measure of water (say a bucket full at my next water change, to ensure enough volume so that adding bicarb won't mean needing micrograms), add some bicarb to alter the kh to a readable level, take ph immediately and then again after 24 hours or am I better adding the bicarb to the total tank water and if so, how much for 55uk gals?


ta
Stu

 

[Themuleous]

Thats exactly what I mean add a few teaspoons to the bucket that should do the job, it doesn't matter what KH you end up with as the pH/KH relationship is fixed. Leave it a minute or two for the pH to settle, then test the pH. Then leave it 24hrs and test again. When you do the first pH test it would be worth checking the KH as well, at least then you can use the CO2 chart to work out roughly what CO2 is in the tank

Sam