What's wrong with my kuhli loach?

[Lizzietheloach]

I have 16 kuhli loaches in a 32 gal that is fully cycled and has been up and running for about 7-8 months. This morning I found one of them lying on his side on the sand. He's struggling to move and his gills are flaring violently. I checked the parameters, which are no different than normal: 0 ammonia and nitrites, 5-10 nitrates, upper-middle 70s PH, 5 GH, 7 KH, 78. 4 degrees F. I did do a water change yesterday, but it was only about 4 gallons for maintenance. I have had some cloudiness in the water in the last couple of weeks, and I changed the active carbon about a week ago. There is an air stone in the tank with the Aquarium Co-Op pump. All of the other loaches are acting normally. I'm sorry for the lack of picture. I turned off the lights to decrease his stress. His colors look great, and I could find no indication of injury. Is there anything I can do to help him? 

Edited July 20 by Lizzietheloach

[Jovius]

Do you have any photos? It sounds like ammonia burn or it could have been injured somehow.

[Lizzietheloach]

Sorry about the quality. I wanted to keep the lights off, just in case it helped. I thought about ammonia burn, but I don't see how it could be that, since I've been regularly testing for ammonia ever since my tank water got a little cloudy a couple weeks ago. It's always been 0 ammonia, and the other parameters have been constant, except the temperature was off by one degree after my water change yesterday. I checked him for injuries, but didn't see anything. All I could think of was that he went into shock, but I don't know why and all the other fish and shrimp are acting totally normal. 

 

 

Edited July 20 by Lizzietheloach