Re: pH Controllers...how to maintain a CO2 level AND pH leve
pH controllers are widely regarded amongst many planted tank enthusiasts as a waste of money and may actually do more harm than good.
They rely on the pH/KH/CO2 relationship to determine CO2 levels.
You need to test your KH (which is rarely accurate using most kits) to determine what pH your controller needs to be set to, by using a pH/KH/CO2 table.
When the pH controller detects the pH is too high it injects CO2 via a solenoid until the pH drops to the desired level. When the pH is low enough, the CO2 injection is stopped.
The issue with this is that CO2 is not the only influence on pH in the aquarium. This is why we don't just rely on the pH/KH/CO2 charts to determine CO2 levels either. Other acids from organic matter etc. in the aquarium will falsify results.
Also the nature of the pH controller continually switching CO2 on and off via a solenoid means that the CO2 won't be stable. Unstable CO2 causes algae.
The pH probe attached to the controller requires frequent calibration and if faulty can result in overdosing or underdosing CO2. At worst this may kill your livestock, at best cause you algae.
It is much cheaper and arguably more effective to use a long-term CO2 testing method such as a drop checker with 4dKH solution.
Check out Clive's excellent article -
http://www.ukaps.org/drop-checker.htm
My advice it spend the £200+ on something else.