Sinking Pearlscale

[Lion_heartx47]

I went on vacation for 5 days and left my mother in law in charge of feeding my fish. Mistake. She means well but I got home and my tank looked as if the entire bottle was dumped in, food coating everything, cloudy murky water, etc. But the worst part is I see Mr. Silly-scales sunk to the bottom. He gets little bursts of energy here and there and will make a break for the surface but will quickly sink back the bottom.
My tank has been established for almost 5 years with no deaths other than my albino ancistrus.
I bought a heater to try and raise the temp a little more, hoping it might help. I'm wondering if "fasting" is legit. I also have another goldfish in this tank and a baby ancistrus. Both doing fine.
Ugh helppp

 

[toolman]

Would do a large water change immediately, siphoning out as much gunk as I could. That food is going to start decomposing and turning to ammonia. Test water, recommend Api freshwater master test kit if you don't have one, and you can do water changes every 4 hours. I would recommend smaller ones after the first one, unless your water quality starts going down, siphoning more gunk out each time.