Red Tailed Shark And Rainbow Shark

I had my red tailed shark and 4 rainbow shark. All of them are slowly dyeing off from some sort of illness while other fish that are in that tank like my cory cats are unaffected. I have one shark reminding and its not doing well, so is it possible that they have some sort of illness that only effected shark please reply with any input. ph 7.0 a 0 nitrite 0 nitrate 5 tank is fully cycled and all shark have no wounds from fight or etc.

 

I may be completely wrong, but they are a loach I believe,kind of like clown loaches etc. And again I might be wrong, but I think they don't have scales. So they're a little more susceptible to illness. I know clowns often get ick and all when people first get them. Maybe you can try to quarantine them and use some medications. But on another note, unlike some of the other loach species, red tails and rainbows shouldn't be kept together or of multiples of the same type. (more than one red tail or rainbow). As they age, they're not wise to house together. Territorial, and aggression can become a problem.

 

Was one of the fish new to the tank? If so it’s quite possible that new fish brought a disease and eventually killed the rest of the village.

 

What size is the tank? What other fish are in it?

 

I've had both Red Tails and Rainbow shark, so yeah your water parameters seem good but they are more susceptible to illness because they are scaleless and are often the first fish in an aquarium to show problems (not to say your other fish will develop problems). How long have you had them and how big is your tank? My first thought is both Rainbow sharks and Red Tails are highly territorial and you should generally not have more than one in a tank unless they can claim their own territories. Mine developed a special bond with my botia but generally they will chase whatever fish is in their line of sight. That being said their temperaments are highly variable between individuals, in my experience, some are much more docile. My guess is they may be developing illness due to prolonged stress because of their proximity to each other. How is their behavior? are they chasing each other? In a large tank they may be okay in bigger groups provided they sort out their personal issues properly and a good broken up environment is provided. They need places to hide, caves, driftwood, heavy plant cover to call their own and feel safe.

*Just noticed I'm a bit late on a reply but hopefully it helps someone.