3 fish dead in 2 weeks and it does not look good for the rest

[naesco]

It is almost impossible to say whether it is ich or marine velvet from your picture.
When you look at the fish lengthwise do you see tiny salt-like specs on it?
If that is the case it is ich and what you need to do immediately is treat the fish as the infestation is serious.
Here is what you do.
Soak dry food like flakes in garlic extract from a health food store or garlic extreme from a LFS. Dry food because it soaks up the garlic much better.
Feed only garlic soaked food as the idea is to put as much garlic in the fish a fast as possible.
Feed very often, overload the fish with this food for the same reason.
If it is not salt like specs you have marine velvet and follow the advice given in the other posts. IME marine velvet kills quickly from the first signs and I note you say that they are dying over a period of 2 weeks.