How to lower ammonia levels
I did a really big change to my 20 gallon by adding fluval stratum. I took my 6 serpae tetras out and about all of the water and plants. I put everything back in but put about 50% new water. I took tests and everything was the same, Nitrate: 20, Nitrite: 0, Hardness: 150, Alkalinity: 80, pH: 7.2. Except my ammonia levels went from 0.25 to 0.50. How can I lower them, or can my fish go back in with the ammonia raised. Also are any of the other levels not good, I am really new to keeping fish.