They are all dead but one. Even the little baby was belly up a few days ago.

All I have left is my "Big Blue" - who is an African Kenyi, the mean one of the tank.

The ammonia levels appear to be what killed the others and I can't figure it out. I've been swapping water out every few days. I did 50% the first time, and have been doing like 30% changes every other day. And yet for a few weeks now, the levels remain alarmingly high. I test the water out of the faucet and it's perfect. I test it daily 2x and it's ammonia through the roof.

I've been cleaning the gravel, but slowly as not to kill off all the "good" bacteria. I only have now like 2 mountain looking rocks. I'm running 2 filters, one of them being a Fluval canister style which is enough for 2 of my tanks. All the media in there is fine. I've even added some zeolite crystals a bit back, as it's supposed to help lower ammonia.

By now I must have changed 100% of the water three times over, and yet the levels still remain high. I don't want Big Blue to croak on me!! Here's a pic of him, in case he croaks soon too. The shine by his gills are normal, been like that since he/she was a little one. Weird as they come and go. Same as the black stripes, they come and go.