Rainbow fish dying off one by one. Heavy breathing and slightly swollen belly

I bought some rainbow fish about 2 weeks ago now. I went to buy them a week or so earlier but they had a few spots of ich. I went back and they were cleared up so I added them to my quarantine tanks.
A couple days later they had a few spots of ich. So I added ich X but my other fish didn’t handle it well so I increased the temp and added some aquarium salt. No fish had more than one or two spots of ich in it and it’s cleared up again. I have been clear for about a week or so.
Last week my pleco has a very bloated stomach and died very fast. Then a few days later one rainbow fish had a bloated stomach and died. It’s been good for a bit(3-4 days) but now the other rainbow fish have ever so slightly bloated stomaches and a breathing super fast.
I don’t think it’s dropsy because they have no other signs of that. Any thoughts fish folks?

I added some Furan 2 Incase it is dropsy.

 

What type of rainbow fish?

 

Blue eyed fork tail rainbow fish. Sorry I forgot that.

 

I’m assuming everything else in your tank is normal? Water, no other recent natural decor additions..

 

Water parameters are great. Normally even zero nitrates. All other fish are fine. I have some danios in there and some green tetras. A couple badis and two half beaks. I planned to add them all to my 75 display at some point. Nothing changed decor wise. I did a water change today but I did it like normal.they all ate except the kids e that’s panting the worst.

I didn’t add salt to the water change water. Do you think it could be osmotic pressure difference. I did my water change at 10 am and just noticed this a bit ago. Also it was a 25% water change and I added the new water fairly slowly.

 

Are there a lot of bubbles in your t ank? Air bubbles? I’m not sure if you’re temperature matching your water changes, but cold water when added to an aquarium can potentially cause some issues. I’m kind of stumped so trying to think outside the box

 

What are the test result for ammonia, nitrite?

 

What are the test result for ammonia, nitrite?

OP stated that water parameters are great and is even seeing 0 nitrates

 

I do temp match my water change water. I check temp before and after the water change and it didn’t even change 0.5F this time around.

just checked since it was a few days since last check and ammonia and nitrites are zero. Never even measured 5 nitrates in this tank.
The one breathing super heavy is at the top of the tank and one other is having trouble balancing. It’s swimming vertically instead of horizontally and it floated up about 3-4” and didn’t seem to do that on purpose. Now 3-4 of the remaining fish a breathing heavy. I fear they don’t have too long. Shame they are cool fish. It’s fairly weird that this is coming on all the sudden. Just did a large water change in my 75 and no issues in that tank.

 

I was headed in a rare and strange direction thinking about a possible gas embolism, but I guess not. I’m kind of stumped. Sorry I know that’s no help

 

I was headed in a rare and strange direction thinking about a possible gas embolism, but I guess not. I’m kind of stumped. Sorry I know that’s no help

No worries. Me too. I’ve kept fish for 25 years and never seen anything like it. No marks at all on them. No internal parasite signs. It’s weird.
If it was something I did with the water change I’d think the badis and half beaks would be more sensitive than the rainbow fish.

 

It's possible that you just bought bad fish. If the fish store had a centralized water filter system it just passes all the pathogens around. I would check out the fish stores refund policy.

 

It's possible that you just bought bad fish. If the fish store had a centralized water filter system it just passes all the pathogens around. I would check out the fish stores refund policy.

They don’t have a centralized water system. Every tank is stand alone at the LFS. Also I’ve had these fish for about 2 weeks now.