pH controller

>For controlling CO2, temp, lights and fan, and so on I'll be using a data
>aquisition card, an old PC, solid state relays, and I'll write the code in C or
>Do have a question though for those of you with pH controllers.  How precisely
>is the pH controlled by these?  I have seen some with +- 0.02 but am unsure
>just how precisely I should control the pH of a tank.  Is 0.1 enough or should
>I use finer settings?  I can control it up to the precision of the probe
>itself, but just do not know if I need to or if I can use a wider range of

A pH controller is something I have been interested in getting for use as
mentioned above. I only found very expensive pH-probes though. Does anyone
know of a good one, and at what appr. price?
Med vänliga hälsningar / Yours,

                    Sven Stenqvist

                    Royal Institute of Technology
                    Tel 08 752 1223.