 Re: CO2 24/7 or timed with lights
i run mine 24/7 but i use a ph controller so it rarely if at all kicks on at night.
i did make a fatal mistake recently, im kinda new to a planted tank, with co2 inj.
i was tring to raise co2 levels up from 2ppm when i started the system 3 weeks ago. i slowly lowered the ph from 7.6 to 7.0. raising co2 to about 10ppm with a kh of 4. temp 78deg. well being a little new i heard 15-20ppm was the target. so over the next 3 or 4 days i lower the ph to 6.5 co2 looked like around 16ppm, so im thinking everything was ok. WRONG. not thinking for the d.o levels especially at night, which at the time a had no way to check. i noticed a few of my angels acting lazy. by the next morning they were both dead along with my 6 year old pleco.
so i immediately did a 30% water change and raised the ph back to 7.0. turned on the air stone to run as soon as the the lights went out.
finally i received my d.o. meter. but i think i already corrected the problem.
last night i checked the d.o with the lights on it read 7.5, seems to be about right for freshwater at 1000ft over sea level. this morning i checked it again,i guess morning will be the lowest d.o. levels, and it was down to 6.5, still ok at far as i know. but id like to keep it a little higher so i am adding a powerhead with a built in air stone to run on the other side of the tank. well see how that works.
what i think happened was.....
in the day everything was ok with the lights on, but at night i was tring to add more co2,bad idea, plants were consuming o2. the d.o. must have spiked to next to nothing. maybe to 2 or less. unfortunatly i had no test kit to verify but im sure that is what happened.
right now the co2 levels are high enough at 10 ppm at 7.0 ph. i could lower it some to increase d.o during the night cycle. i will try the powerhead first and see if that helps. | 
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