Cyprinodae Diseases?

So I had a molly that was fine for months then acted very very weird for a week, his fin just started rotting, I cured it and then he randomly died. Now my rainbow shark which is also in the same species group is acting very weird with no bloating or pineconing scales. He won't eat either. He just goes in one place of my tank all day and swims sideways. I've tried everything what can it be?

 

How big is the tank, the rainbow shark and what are your water levels reading? Also what other fish do you have in there with the shark?

 

55 gallons
0 ammonia 0 nitrite 50 nitrate (always at 50 or higher due to city's tap water"

X2 angel fish
X2 golden panchax
Earth eater
Mbuna chiclid
BN pleco
X5 rummy nose
Rainbow shark

And the rainbow is around 5 inches

 

Are you sure that the cichlids aren't beating it up/tearing it's fins or stressing it out? Also, is there any medication still in the water from treating the other fish? Do you dose with prime? What are you trying to feed him?
I've got a rainbow shark about that size too, he will only eat veggie wafers and only when the lights are off and the cichlids are sleeping. He also will clean the rocks I have in the tank and swims upside town on them, kind of like a pleco.

 

The chiclids may possibly be beating it up and the only meds I've used in this tank is melafix and yes I use prime after every water change, and he's always ate crushed up spirullina flakes and minI veggie pellets or he will just eat away at a veggie round I put in the tank

 

Can you take a picture, it might help. Hopefully someone else will be able to help you as well, I've got to get some sleep.

 

 

Are his gills always red? There is a bit of white stuff at the end of his tail, is this normal and it looks like he is getting fin rot possibly. Mine is a just a regular black one.

 

Yes his gills are always a shade of red due to him being albino, that white stuff is scale damage and that is a possibility

 

I've not dealt with fin rot yet, I think I have tetracycline flakes for that though. If it is columnaris I treat with the kanamycin sulfate flakes. When I was first getting into fish keeping I got the Melafix and Pimifix... They aren't "medications" though, and I didn't have much success with them. I went to Amazon and got a thing of 5 different pre-medicated flakes. So far they have all worked wonders except with the nasty red anus worms!