Thank you all for your answers!
I'll limit the light and look at getting some aquarium plants, as I've been meaning to anyway so the fish have some more interesting things in their environment.
I had a quick look up about mosquito fish too, and I think that might be what they are!
I used to have an aquarium a few years ago when I joined this forum.
I now have a little project going on, but its been a few years so I need to refresh my knowledge.
So, I have what I believe are 5 wild guppy - they are an invasive species around the rivers/lakes where I live...
I have a 20 gallon aquarium that has 7 harlequin rasbora, 1 male betta, 1 apple snail and a BN pleco.
recently I have noticed that my bettas fins looked torn, and a few weeks ago I saw why - my BN pleco had been attacking my poor boy while he was trying to sleep on the bottom of the tank, so now...
Thanks so much, I'll add some shells and cuttlebone as I have them on hand. I tested my water and my results are:
I don't know what my KH is. I see what you mean about the nitrifying bacteria not being able to process the ammonia as well...
So, I have been giving him Epson salt baths, fasting him and feeding him peas but he still hasn't improved nor has he gotten any worse. Still quite active and has an appetite, he has done maybe two poops in the last 2 weeks or so.