http://www.prirodni-akvarium.cz/en/index.php?id=en_co2ph. Plenty of good information and a good example of pH readings according to different setups.
Good information but the second last sentence makes no sense, 'Aeration using an air stone has [despite the widespread myth] virtually no effect on CO2 degassing.'
This is precisely the solution I use to allow me to balance my co2 levels.
My DIY reactor gives me 100% co2 dissolution but because I'm using a canister and not a wet/dry filter my O2 saturation drops due to the small surface area of my tank (28L) and the fish aren't able to tolerate the level I need to get to for my drop checker to go green/yellow, so by lights off the fish are all at the surface. I then introduced an air stone at lights off to degas the co2 quickly and hopefully add some O2 before lights on again. I have been using a pH controller with my gas set at a level so that I go from 6.8-5.5 in two hours before lights on and the controller switches the gas off, but its not low enough to turn the drop checker green/yellow without the fish gasping. At a rate of injection to get that drop in the two hours before lights on, my solenoid was only ever open for about 3 hours total after lights on out of a 10 hour photoperiod, co2 degassed that slowly, add aeration at lights off and the pH climbed 0.5 in about an hour and fish became active again.
Cue aeration 24/7 and an increase in co2 injection rate (approx x3). Gas comes on same 2hrs before lights on and the pH rapidly drops from 6.8 to 6 in 15mins but due to the aeration it tails off and only finally makes it to 5.4 by the time the lights come on. This ensures the drop checker is the correct shade of green to be nearest the 30ppm level. To ensure that my off gassing rate and injection rate balance to keep me around 5.4 (the variance in my controller will close the solenoid at 5.31) I can either fiddle with my needle valve or adjust the amount of aeration, I did both. I added a flow clamp on the air line and dialled down the aeration injection first before I touched the needle valve on the co2, it was then a case of fine tuning both over a few days to get the sweet spot. I'm now using aeration with an air stone to control my off gassing and not touching the needle valve at all, I'm chewing through gas for the entire photoperiod without the solenoid being triggered to close.
So judging by my observed experience that's why that statement makes no sense to me. The air stone is increasing the area that my tank water can make contact with air beyond what my tanks surface area alone can without aeration. It is also providing a surface agitation, but not much more than my 900lph filter is putting out so my observed effects can't just be down to minor increases in surface agitation. The best method for aeration is a wet/dry filter, which is water crashing through an air interface. An air stone is air crashing through a water interface.
The key is to ensure you have enough O2 in the water relative to the amount of co2 you inject, then you can stop worrying about the fish and concentrate on making sure the plants get what they need. I needed to use more co2 to ensure I have enough O2 in my tank, crazy but true, but now the fish don't care!
My KH is probably close to zero, and I'm off the charts, but my pH drop still correlates to the charts.
