lol i use to work at my old LFS when i was in high school same thing..... feeder tanks are the worst

your Right i will calm down lol as long as my waters good

What kind of Rainbow did you lose?
I went through 1/2 a school of Threadfins before I figured out it was chlorine-burnt gills. I was adding Prime as the WC happened.
I then started pre-mixing and problem solved. It did quadruple my WC time though as adding 50g from a 15g tub took much more time.

+1 to wasting CO2 @ night
Running it @ night can cause deaths if you don't have enough surface agitation/air injection -stones, venturi powerheads etc.
Having your CO2 on a timer set to turn off about 1/2 hr before lights out and come on about 1/2 - 1 hour before lights on is usually the best recommendation.

Your plants will process CO2 through photosynthesis during daylight, during the night, they actually use up oxygen.
Running CO2 at night is both wasteful, and significantly lowers the amount of oxygen in the tank, usually resulting in death.