pH, kH, and CO2

[RockabillyChick]

i just got a kH test. and i just started injecting DIY CO2.

my tap has pH 7.8 and kH 5
my tank WITH the CO2 ON, is pH 7 (havent tested kH with CO2 on yet)
my tank with CO2 OFF, is pH 7.8 and kH 5

what is bothering me is that it seems that the pH is fluxuating too much. should i be leaving the CO2 on all the time to keep the pH stable? thus far i've been shutting it off at night. i had it on yesterday and my pH was 7 i got a kH test today and right now the CO2 is off and the lights are off and my pH is back up to 7.8 and my kH is still 5. this isn't making sense to me >_<

 

[Needeles]

Yes you need to leave the CO2 system always running, day and night. Best thing to do is get a small air pump and air stone and turn that on only at night. This will keep the oxygen levels safe for the fish. This will also help keep the pH from swinging so much.

 

[wesleydnunder]

I have a similar swing in my 125. Ph 7.0 with co2 off to ph 6.6 with co2 on. Tapwater is ph 7.6, so not all of my co2 off-gasses at night. I run my co2 solenoid on the same timer with my lights. I have discus in this tank and the ph swings don't seem to bother them. According to RTR and others on this board, fish can't read ph, so ph swings as a result of co2 injection shouldn't hurt your fish. IMO running your co2 at night is a waste of money since plants dont use it at night. On the other hand, it takes a couple hours to get my co2 up to 30 ppm when the system turns back on in the morning so I don't have good pearling until then.

Mark

edit: Also, Needles, it occurs to me that running an airstone will cause co2 to gas off and cause SOME ph shift as co2 level drops.

Mark