Advice on Camallanus and a twisted spine

[actin]

Hello everyone.
I've been having problems with my freshwater aquarium that it have been difficult to find sure advice on. For most things the internet seems to say both yes and no to everything, but I was recommended this forum as a better source.

I wasn't able to find anything already on here, so I'm going to simply describe my case history and hope someone can comment, with my apologies if this is a retread. I have a large tropical community tank with live plants, many little snails, but by now not too many of its original fish.

So this year I started adding new ones, and bottom-dwellers have done well, but over a month or two most tetras and dwarf neon rainbowfish began to fall ill and die in succession. At first I thought the problem was shrimps that started eating them, but giving them away, microscopic inspection of corpses revealed that at least the rainbowfish had red Camallanus worms inside them.

The tank was treated was Praziquantel, two or three times, but a while later the second last rainbowfish suddenly died and again had worms. So I've followed a suggestion to dose the tank with cupramine, and have just recently finished cycling it.

Here then are the questions I don't know about:

1. I had removed many snails before treatment to avoid creating lots of dead material, and since I find them nice to have. As it turns out, most of the ones left behind lived through the month of cupramine; and afterward I thoughtlessly put a few others back, only then realizing I don't know if they can be carriers.

How much of a problem is this? Does the snails surviving the treatment mean something has gone wrong, and how much risk might the treated/untreated snails pose to fish? Does there need to be any additional treatment to the main tank, or the spare one full of snails?

2. The reason I became worried is something has happened to the last rainbowfish, but it's something different. One day I found him with his spine bent, stuck in sort of an S-shape, but side-to-side rather than up-and-down like you see in inbred fish.

He has been in quarantine for a few days; I have no good way to inspect for worms, but he hasn't shown any marks or symptoms of weakened fish. In fact he's still fully active, and even excited for feeding. Except he doesn't swim properly and even if nothing else is wrong yet, I'm not sure if he is able to actually eat anything.

The people I talked to have never heard of this, and I wouldn't know how to look it up. Is there an outside chance something can be done for him; and more importantly, is this an injury, a symptom of worms, or a new illness that might provide risk to the other fish?

Sorry for being so long-winded; I imagine it's poor etiquette for a first post, but I have no ideas what sort of details might be useful here. Any help you can give me will be greatly appreciated.

Kind thanks.