There always lots of folks just starting the trip down the CO2 path and most do agree there is a pretty steep learning curve involved so I thought I might post this warning.
It can all go bad and sometimes it does it really quick! I thought I had a handle on making changes really slow and gradually but that was not good enough today. I came within a short of killing the whole tank and I'm still working out what went wrong. One thing that made recovery much harder was that I did two things at once. I should know better!!!
One was a 50% water change and that used up my reserve water supply so that my new water was still cold. Water lines here are not buried deep so the new water in the barrel was about 60 F.
I normally treat it and let it warm up before I need it in the tank but today was a total wreck.
After the water change, I bumped the CO2 just a touch and that was too much. I have a 120 gallon and using a Grigg's style reactor, I push too many bubbles to count so adjusting is just a small touch that can't be seen to count the change.
I was here and watching but within two hours I had major trouble with fish nearing death.
With lots of new water, adding hot water from the sink to maintain a reasonable temperature, and lots of powerheads and circulation they have all recovered but it was a close thing.