Bro, just share some exp. Try lower your SG to 1.020 - 1.022 slowly. Fish like it low, low salt means their body work less hard.
Do you want to try doctor G anti parasites cavier? google it for more infor. I personally feel it is useful.
Lastly, try changing 10% -20% water daily, till the fish mati or recover, whichever comes first.
P/s: if you have a bottle, i can pass you a qtr of doctor g anti parasites to try it out.