I have 15 kuhli loaches in a 32 gallon planted tank. Most of them hang out all day and sift sand, lie in piles, or explore, but 4-5 of them hide regularly. Yesterday evening I saw that one of my newer loaches is very skinny. He came out during feeding time, but it didn't look like he was actually eating, just sifting sand next to the food and the other loaches who were eating. I test my parameters regularly, and they are all normal today - 0 ammonia and nitrites, low nitrates, 77-78° F, stable pH and hardness. Is this a parasite? Should I treat the tank with something? I do not have a hospital tank, so I was thinking of treating the entire tank with ParaCleanse 2 or 3 times after watching Cory's video on that medicine. I don't have a picture of this loach, because he's one of the few hiding ones and he was only out for a little while, but just imagine the skinniest little slip of a thing, so skinny you could almost see right through him from the side. I didn't see any other visible issues. I got him about a month and 1/2 ago with a group of small, young loaches. They are mostly still small, but definitely not skinny like this one.
I'm feeling sensitive about my loaches because we lost one a couple weeks ago when it went into what looked like shock for no apparent reason. We euthanized it after it didn't get better because we didn't want it to suffer. I can't help but to wonder if this is a similar problem, but I don't remember that one being as thin. The ParaCleanse arrives tomorrow.
If I do dose the tank with ParaCleanse, how many times should I do so? I have a Fluval Flex, so I have active carbon and biomax. Should I remove both or just the carbon? How do I store the carbon while I'm medicating? What can I do to keep my cycle from crashing?
Sorry for the all the questions. This will be my first time medicating a tank, and I'm nervous, but I really care about my loaches and want to help them.
Thanks so much.
Edit to add that the whole tank has kuhli loaches, zebra danios, and amano shrimp