Hi guys! I am new to the fish keeping. I recently started. I have a 20 gallon tank long. I have a whisper 40i filter and a preset tank heater 100wt. I have 3 Cory's, 1 beta, 3 balloon rams, 2 mollies, 8 cardinal tetras, 6 platies. I have tested the water I have gotten everything good but the...