Today is the third day after I did the water change. I changed 80% and I found ammonia in my water. It's about .50 ppm. I didn't feed the fish in the first day either. Any idea why it happens?

Is the water green already or still clearish?

it's green already

Hmmm no dead green algae particles floating around? Maybe u got a piece of poo in the test tube

I would wait until 2moro and test again. Should only be a little ammonia spike.

On another note, I think another pic of your wonderful setup and the fishies is in order

Thanks buddy. I will post the pic ASAP.