I just recently did a water change for about 1/3 of the tank, introduced a moss ball, and a now dual air/bubble wall setup as well as a submersible heater and thermometer replacing the overdue-falling apart filter cartridge out, with the new carbon but keeping the cycled driftwood plant piece alone and minimally cleaning the walls of the tank. My fancy tail was having issues with her swim bladder which I feel was due to over feeding and or malnutrition which prompted me to make some changes and monitor her eating. She got better and is now good ☺️ However when I got home from work I noticed red spots almost like an ammonia burn or something of that nature so I test the water and it's still high almost the same as before the water change. Around 2-4ppm from the test... I have a 20 gallon bare bottom tank, dual bubble walls, Whisper filter, submersible heater and a hanging submersible thermometer with the driftwood piece and a moss ball. I only feed her once a day as to not have any issues with her swim bladder and she's about 3 1/2. Hope that helps.