Sick Pleco

[Stefano of Gregorio II]

I have a Pleco thats is very sick. One of my plecos just died about a 2 weeks ago suddenly without any signs of illness. Now, the one I have left has lost all of its color, doesnt eat and doesnt move much. He doesnt have any marks or dots or discolorations of any kind on his skin. The same time I noticed that the pleco was acting strange, my Bala Sharks had developed "foggy" eyes. I figured the sickness was somehow related so I bought "lifeguard" dissolveable tablets that say they treat almost everything. The "foggy" eyes went away on the Balas but the Pleco only showed improvment for maybe 2 or 3 days then back to sick. The symptoms I have for this Pleco span just about every illness there is for fish(not eating, loss of color, minimal movement) so i have no clue how to treat this poor fella. Can anyone help, i would appreciate it.

 

[WILDER]

Need more info.
Size of tank in gallons or litres.
How many fish and which type.
Water stats in ammonia,nitrite,nitrate, and ph.
Cloudy eye is a symtom of a desease not a desease in its self.
Poor water quality, stress, bad diet, old age, parasite to bacterial infections.
Pale skin is a sign of stress, bad water quality, parasites to bacterial infections.
When fish don't eat not a good sign, is he bloated or wasting away.
Can you see what it looks like when he goes to the toilet.
Also is he laying to oneside on the substrate.