I'm not even sure if my sick kubotai loaches have the skinny disease or not. They are appearing listless and are panting heavily. Water conditions are perfect (6ft tank, only about 35 small loaches in tank, so a very low bio-load). Most other loaches in the tank are not bothered at all. I lost my first loach in this tank over 3 months ago, but since I found it floating (probably within 24hours of death), I didn't really have much to go on. Then over the last 2 weeks I've noticed a few of my other kubotai are panting and listless. One of the little Dwarf Chain loaches is also really pale, but at least it is still active with the other sids.
10 days ago I dosed the tank with levamisole. I went with 2mg/Litre of active ingredient. I worked it out to require about 36ml of the "Big L" Pig Dewormer that I have. I left the dose in for 4 days. I have since done two very slow water changes. All fish seemed to love the water change.
I lost one of the most listless of the loaches just after the water change. There are still two Kubotai who aren't doing very well.
I have now tried to remove all the driftwood from the tank, but the loaches love hiding in the holes and gaps of the wood and not moving, so it is frustrating to say the least. Their tank is 6ft x 2ft, and that gives them a LOT of swimming room for a bunch of very quick little fish. Catching the sick looking ones is not going to be easy, but I will be trying that tonight. They'll be going into a quarantine tank once I do get them out.
Can someone help me work out what might be wrong with the fish, what I should do to help them get healthy again, and what I should do immediately to help me from losing any more of these great fish. (Not to mention that they cost $30 AUD each).
The below fish is the one that finally died. It doesn't look as crazy skinny as the yoyo loaches that I see in shops. But, it is no where near as fat as the other 15+ kubotai that i have in the same tank.

This is the levamisole product that I used:
