There is no reason to dose with prazi pro. This is used to kill parasites, there is no indication, from the info you have provided thus far, that there is a parasite infestation, and thus no reason to add a poison to the tank.
How long have you had this ray?
How long has the tank been running?
Tank size?
Other tank mates?
It just sounds like, what others have mentioned, that your water is not "clean" enough, either it is overstocked or under-filtered.
Your ray will pull through this fine if you keep the water changes up and the temp higher than normal and the salt helps as well.
i have this ray for 2 years now. this is the first time it happened. it has only one tank mate (arowana) and it's in 90 gallon tank. it seems to do better tho, thx for all ur help