If the ray can sit with his disk flat then it's not death curl, which is very good. The tail looks like it is a fungus, when you go to buy a test kit tommorow also buy some prazi pro to treat it. The salt will also help this. Make sure to turn the lights off and possibly put a blanket over the tank to reduce stress. Also, I would recommend you buy another filter, preferably a canister. Good luck
Also forgot to add fatten that ray up! start feeding him more blackworms so that he gains some weight, its great that you've gotten him to eat silversides already within a week. That's quite an accomplishment especially with a retic.