Most people w/out pH controllers leave it on for 24 hours. This reduces pH swings caused by running it on a timer, but if you do this you have to keep your eye on the kH to make sure the pH doesn't crash.
I use a ph controller. I recently tried to use a timer instead, but in my tank, the ph keeps going down even after 5-6 hours. That means I won't be able to get a stable/high C02 level most of the day. Went back to controller I believe 24/7 is better than on a timer for good level of CO2 during photo period.
ok, found my problem was with needle valve setting. Now I put my ph controller on the timer, works great.
I leave mine on 24/7. I also believe that PH swings are not a problem at all. I think only extremely high CO2 concentrations are something to be worried about. I've had mine up to a level higher than I'd like to admit and did not notice any problems with my fish.
Just during photoperiod here. My rationale behind this is the plants will give off CO2 during the respiration phase, that would increase pH swings during the night if CO2 was injected. Maybe i'm wrong, maybe they don't give off that much CO2, I have never monitored my pH for a complete 24hr. period.
I can add a lot for the photoperoid rather than a sustained chronic level that is going to be more harmful to fish, bacteria etc and it adds a measure of safety should an over dose occur and also saves on your gas if you use Gas tank CO2.
DIY is easy to do this way as well.
We add CO2 why?
To fertilize the plants, not to control pH, pH is just the measurement to determine the CO2.
You do not need CO2 at night at all.
The fish are not as concerned about the pH as they are about the alkalinity and GH.
FYI, pH changes are enormous in aquatic plant ecosystems, 2-3 units are common in shallow planted lakes, some times 6 to 10 in some cases.
Recently I traded wagons. Switched from 24/7 with pH controller to CO2 on only during photoperiod. My tapwater parameters recently changed, and I can get a pH swing of 0.8 every water change. Fish can't tell the difference.
I just recently set up a pressurized CO2 system and have since cranked it up to nearly 1 bubble every second for outstanding plant growth I never even got close to seeing with two 2L DIY bottles. Mind you my planted tank with the press CO2 is a peaceful community 10G running 40W of PC lighting and I also add lots and lots of a liquid mix of H2O/KNO3--I've found it easier to control growth than adding dry KNO3. Oh and lots of plants--thanks Travis.
Not really sure if it's the low pH as I leave it on 24/7, but since then I've lost two of my emerald grn cories just out of nowhere and I haven't lost a fish in this particular tank in a long time. One of the black skirt tetras is almost 2 yrs old.
pH death or something else? I've got extremely hard water. Mineral deposits in the toilets and bathtubs in my house every week. Thanks!