I've had my turtle for about 3 months and he has been perfectly okay until last week. The tank is very clean, I just turned the temp up to 80 because I think he is sick. He has only gone into the water a couple times and when he does he sinks to the bottom and doesn't do anything. I saw him struggling to get back onto the basking area so I helped him up. I have all the right equipment. I've been trying to feed him his staple food but he ignores it, I have also tried shrimp but he just doesn't even look at it!
I thiiink there's a little mucus on his nose. His shell looks fine, my boyfriend thought he was just being lazy but definitely not.
There's also another turtle in the tank and I don't see her interact with him at all so I don't think she's a problem. I've tried feeding him without her in the tank and he doesn't do anything still. The girl is significantly larger than him too. I can't tell if he's grown at all since I got them both.
I don't know what to do. Any suggestions!?

