CO2 controllers, pH & fish death?

[gvildawg]

A thread I started over in the general freshwater section got me thinking about this. I have a pH controller. It is hooked to a timer with my lights. When the lights go off so does it. When those go off my airstones come on. I run 8 or so hours of lights/CO2 and 16 hours of airstones everyday. There was no reason that I could see to be adding CO2 without light so I figured "why waste the CO2?" My natural tapwater pH here is around 7.6. My CO2 injector keeps it around 6.6 when it is running. The question is this--could the pH fluctuations caused by cycling off and on the CO2 be killing my fish? I've been running my setup this way for 4+ months with no problems until I had a unexplained nitrite spike last week. Now I'm wondering if I have been slowly damaging my fish all along by cycling the CO2 before I even had the nitrite spike that cost me about a dozen fish. Should I just leave my controller on 24/7 and let it add CO2 as necessary to keep my pH in the same range all the time?

 

[gvildawg]

I got my answer on another thread with a link to plantedtank. Thanks IceH2O!

 

[Rex Grigg]

Kind of a belt, suspenders, duct tape and staples kind of person.

pH changes caused by the addition or removal of CO2 do no harm to fish.

See www.theplantedtankFAQ.com for info on why that is.

Having a controller attached to a timer doesn't make a lot of sense to me at all. Actually defeats the purpose of the controller. And then running airstones?

I ran CO2 into my tanks 24/7 for years with no problem. I now have most of them on timers. The CO2 is on during the lighting period.

 

[gvildawg]

I run the airstones because I am worried about there being a lack of oxygen when the lights are off and the tank is dark. Am I worried about nothing? Is my Rena XP3 filter sufficient to supply enough oxygen when the plants aren't actively photosynthesizing? The controller is on a timer because my CO2 system is totally automatic and I don't see any reason to be dosing CO2 when the light are off. Am I missing something here? My pH rises from around 6.6 to 7.2 in the 16 hours when the CO2 and lights are off. When the lights/controller cycle on the pH comes back down to 6.5-6.6 in a half hour or less.

 

[mellowvision]

from what I've read, running the airstones should be enough to calm your worries... I'm not saying there is an oxygen defficiency and night, I have no idea, but running the airstone will dissapate the co2 and introduce o2... which is what you want in the end. it seems like shutting off the co2 is overkill.

I also imagine, and I'm a noob, that the plants would do better if there was co2 available to them the instant they have light to work with... I read someone having a timer turn their co2 on an hour before lights.