Ok, I am new to the whole aquarium bit; my husband has had one in the house for years but I never paid much attention to it and he has only done bare minimum maintenance. I got a wild hair and decided to try to make the plants look better…. In the end some of the fish died (and the rest may still die) and I’m trying to figure out why. Here’s what I did:

I did a little reading on the Internet and found that we could make our own CO2 injector by mixing yeast, sugar, water in a Coke bottle and funneling the CO2 into the tank via some airline tubing. Long story short, a little bit of this mixture ended up in the tank (75 gallons) due to my ignorance of vacuum. It started producing CO2 within hours which I collected in an overturned drinking glass so it could diffuse into the water.

The other I did is I added some plant food tabs to the gravel. The website I read suggested using the cheaper pond plant tabs rather than aquarium plant tabs.

The morning after we did the CO2 and the plant food the water was cloudy and that evening two angelfish died. I don’t know what the pH was before but now it is really high (at least 9) according to API test strip.

Anyone have any thoughts on what killed the fish/raised the pH?
It’s been 24 hours since I submitted this question and ALL the fish have died…I did a 50% water change when there were still four but it didn’t help. The water is still cloudy….