you only need to add salt if there is actually a problem and the rays are really tough provided the water there in is good.
ive seen loads of damage on rays and in almost all cases its gotten better on its own.
if you do really need to add salt then you can check my thread on stumpy but i would and do only add anything if i think it cant get better on its own, if this is the case then ...
you need to use salt with no addatives (most food grade salts have an anticaking agent in dont use the ones with anti caking agents in)
aparently kosha salt doesnt have any additives but if you cant find it then marine salt is fine. ( in your local pet store for marine tanks )
as for the dosage you will probably get mixed answers and different dosages can be used for different things.
if you look for my thread on stumpy i listed the salt details i used at the time there . i used a little more than was recomended by some so i wont be suprised if people say its too much but i did research as much as i could and stumpy is still alive and well today.
i think in the end i went with 6grams / liter of water but you have to increase to this concentration slowley and not add all the salt at once.
instead mix a bit at a time out of the tank and add the salty concentrate to the tank over a longer period (like 1g/liter increase every 12 hrs untill you get to the required concentration).
for a 240 liter tank you would need 240grams of salt to make 1g/liter. in 12 hrs add another 240 grams of salt to get 2g/liter then in another 12hrs add another 240grams to make the overall concentration 3g/liter. etc etc to the required dosage.
if you do a water change (and i imagine you will be to make sure the water is tip top for the poorly fish) you can calculate how much salt you need to add to get back to the same level but you should be lowering the salt level after two weeks ( i just stopped topping up the salt when i did water changes).
hope it helps
