I've got ten guppies, two plecos, a fire eel, and a half-moon betta in a 20gal planted tank. I've got a Tetra hang on filter rated 20-30 gallons.
Ammonia is nearly 0
PH is about 7.6
Over the last four days, he's been lethargic, hanging out at the top of the tank. Im noticing blood in his fins. My first thought was ammonia poisoning, but none of the other fish are having symptoms.
Everyone gets along great. I don't know what could be bothering my betta. The temp in the tank is 77-79, kept by a Tetra heater.
Take a look at my tanks, Excess is the one I'm describing.