I am hoping for some advice on a fishless cycle. I'm fairly new to aquariums and fish. I'm 24+ weeks into a fishless cycle on a 5-gallon tank (heated, filtered) in which I am hoping to someday keep a betta fish. Records of the cycle data and my specific actions are attached. Unfortunately, the cycle seems to be not working. Or rather, it has at brief times seemed to be working before falling apart. I am not sure what's going wrong and what I should try. For many weeks after I started, the cycle seemed to be doing nothing, and about 14 weeks in I managed to get a used filter from a neighbor's cycled tank. That seemed to kick things into gear, but ammonia was still getting down only to about 0.25 and not 0. Then, after several more weeks, the ammonia finally started to get down to zero. For about a week I thought I was all set, but then my pH inexplicably plunged down off the chart and the ammonia went back up again. After a water change the pH is now up again but the ammonia cycle seems almost back where I started 24 weeks ago. Can anybody find a pattern in the data? Is there something I'm doing wrong? I am mystified and would be grateful for any insights! Thanks.