What's wrong with my fish?

[charlie]

I have a 45 gallon fish tank and i now have three large gold fish and a pleco that are about 3 years old. about a month ago i had a couple smaller fish die (betta small goldfish) and the larger fish started getting lethargic. THey would just hang out on the bottom and tails were drooping. i noticed a sort of slime build up on the glass. about a week and a half ago i did a partial water change (about half) and cleaned the tank thoroughly. They seemed great for a couple days now they look worse than they did before. one gold fish kind of hangs vertically near the surface and his eyes look a little cloudy. my pleco has these little white dots on him that i'm not sure i noticed before. THere are no other visible abnormalities with the other fish. i have a simple test kit for the water and everything looks fine. probably some sort of disease but i don't know how to treat it.

 

[etchemzee]

I also had a similar problem where my Goldfish would hang head-down near the surface. I started doing rapid (every second day) partial (20%) water changes. This although did not prevent the Sick Goldfish from dying, but saved the rest. The problems of Ammonia, Nitrates and Nitrides can be countered with twice to thrice weekly partial water changes. i do not have any test kit, but such actions result in a healthy aquarium. Although it does increase my job many-folds, but I sort of enjoy it.

 

[catx]

What were the test kit results exactly?

Everything you described sounds very much like a water quality issue, the lethergy, muck, death, and the ich parasite showing up on the Pleco.

Test your water again and post results back here, liquid test kits are more accurate than test strips and they do expire, so check the expiry date.

Perfect readings are:
Ammonia - 0
Nitrite - 0
Nitrate - under 20-25ppm

Anything deviating from that will indicate a water quality issue and those partial water changes will need to be stepped up a gear.

Your tank is heavily stocked, Plecos are huge waste producers (and shouldn't ever really be kept with Goldfish), and the Goldfish themselves are also very heavy waste producers. All that waste can screw up the water quality if you're not careful.