I set up a 20L tank for my fish about a month ago. When I set up I put in water conditioner and adjusted the pH to 7, then about two weeks later I realised I should put in some good bacteria, so added that. The fish were in there from the start. I have 4 black neon tetras and had my Betta in the tank. There are three live plants and two rocks. The tank is heated to 25*C, and has a filter/pump set up. I keep a light on above it for 8hrs a day. I feed the fish Betta flakes once a day.
About four days ago I noticed that the Betta was lying around on the bottom and not coming up to feed, then he spend more and more time on the bottom until this morning when he was kind of writhing around in the same spot, again on the bottom. When I got home from work this afternoon he was lying motionless on the bottom and had gone a pale silvery colour, so I assumed he died :(
I have been doing a 20% water change once a week, although once it was two weeks as I went away. I checked the pH two days before the he died, which had gone up to 7.6, so I adjusted it down a bit, but havent re-checked. I wasn't really worried as the Tetras have been fine.
I haven't checked the ammonia or nitrites, as I thought since the Tetras were okay it should also be fine.
I also had a small mirror floating at the top of the tank so my Betta could fight himself if he needed stimulation.
I really want to know what went wrong, as I would like another Betta but I don't want to accidentally kill him, and for now I really miss Percy! :(