Cause of Skinny loach disease?

[squid]

Whats the main cause of skinny loach disease and how do they usually get it?
I noticed one of my clown loaches getting skinny.
I only feed them pellets and frozen fish. dont think there's a risk of getting parasites from frozen fish and shrimp?
planning to dose with levamisole for the whole tank .

any ideas?

[Diana]

The fish can pick up parasites when they are in the wild, or in the tanks where they are held between sales.
Internal parasites may grow slowly, so you may not be aware that a fish is infested. These parasites can be spread among many of the fish in the tank.
When something weakens the immune system of the fish the parasite may grow stronger until you start to notice that the fish is not doing as well as its tank mates. Moving the fish from one tank to another, or social arguments among the fish and other things may stress the fish. Some fish are more sensitive to things that cause stress, so it is entirely possible that one fish in an aquarium will show the effects (Such as Skinny Disease) and others will not.

Most diseases move faster than parasites and a fish with a strong immune system can fight off the disease, so you might not even know there was a disease in the tank.
But a fish with a weakened immune system cannot fight it off, and will get sick. Disease organisms will reproduce, and these increased numbers can spread to other fish, even with stronger immune systems. This can happen pretty fast, so a tank might go from 'nothing wrong' to 'lost all the fish' really fast.
A fish might have a weakened immune system because of a low level parasite infestation, or any other stress.

The 2 problems do contribute to each other, either can start first, and the stress of either can open the door to the other.

As for whether frozen fish can contribute to a parasite problem, I think it can. You should cook the fish to kill parasites before feeding it to your aquarium fish.