Hiya. I set up a 15 gallon tank around 40 days ago and did a fish in cycle (my partner came home one day with a Betta in a cup). I planted heavily with mostly foreground plants, carried out regular water changes (usually 25% or more daily), and tested my water daily. I saw my ammonia levels register, then nitrites began to register, and some nitrates (but only to 5). They didn't have the nice bell curve that cycling charts show, because I was changing the water a lot to try to keep levels down for the fish. After picking up nitrite readings (usually .25 or .5) for about a week, I added a DIY c02 setup and after a few days I stopped getting nitrite readings, but would still pick up ammonia. I realized my pH dropped to 6 or below, and thought it might have stalled or killed the biological filter, so I added crushed coral in my filter to boost my pH to about 6.8, where it has stabilized. After a few days I began to see small amounts of ammonia at around .25, but some days I would get a reading of 0. I have stopped doing daily water changes to see if that helps, but even when I wait 2 or 3 days my ammonia only gets to around .25, and nitrite is not going back up. My nitrate is steady at 5. It's been two weeks since I added crush coral and stabilized my pH, and I'm in a holding patter where some days I have no ammonia, and some days I get a reading of .25. Still no nitrite and nitrates at 5. I'm wondering if anyone else has run into something similar. Did I kill off my biological filter with low pH and the cycle is slowly trying to restart? Am I doing too many water changes? Did my tank cycle but I'm getting ammonia readings from something else? Did my tank never properly cycle? Any ideas on what I can do to figure out what's going on. Thanks in advance for any advice.