Pakistani (Yoyo) Loach refusing to eat

Question
Planted 55g tank, ph 7.8, ammonia/nitrite ~0.  Temperature is 78-80.  Tank running for about 3 months, livestock include 3 clown loaches, 1 red tailed black shark, 5 siamese algae eaters, 1 flying fox, 5 otocinclus cats, 1 black ghost knife, all have been in my tank for 2.5 months.  Onto my question:

I recently purchased 7 Pakistani Loaches, from two different fish stores.  Six of them died within 4 days, all of them prior to their death had extremely fast respiration.  The sole survivor I have placed in a quarantine tank, he too exhibits the extremely fast respiration rate, sits listless at the bottom, and refuses to eat.  I have tried feeding him bloodworms, brine shrimp, flakes, and algae wafers.  I even tried hand feeding him a bloodworm but after running from me for 10 seconds, he gaveup but still refused to eat.  He has been in my quarantine tank for 3 days now.  I have tried Melafix, Pimafix, and an antibiotic the fish store recommended based on the other dead fish's bloated bellies indicating an internal parasite.  The name of the antibiotic is Metrozol.  

Also, the fish's gills seem to be slightly red on the inside.  Because I am not too familiar with the appearance of a healthy Paki Loach's respiration rate or normal gill coloration, I am not sure if that is normal or not.  

Please help!

Answer
Hi Shahid;

It could be a parasite on the gills. The Metrozol treats internal protozoan parasites but not gill or external parasites. Saprolegnia, gill flukes, Gyrodactylus, are all possibilities. It could also be an internal bacterial infection or fungal infection, or the fish all came from the same wholesaler to each store and they were infected and oxygen deprived, or gill damaged before you ever got them. Check with both stores and see if they have any left and see how they are doing. If there are none, they probably died too.

Treatment options are many, as there are so many causes. Here is a link to a chart that may help you figure out what it could be so you know what medicine to look for at the local fish store;

http://www.klsnet.com/files/fishchart.htm

At Your Service;
Chris Robbins