Hey brother, don't worry yet...I've had mags look way worse than that.
Listen, keep flow going but point it up at the surface of the water or block it too prevent direct flow from moving him around the tank. He's gonna be too weak at this point to keep himself stable.
Stick with the plan, make sure ur WC water is salinity matched and heated. If possible, use DT water, then just top off your DT. This will help the Mag and at the same time, your improving water quality in your display tank.
Also, don't move him at all. Only move him if he is face down. Then gently flip him over so he can get light. Moving him around a lot will make him worse. If he is on eggcrate, just leave him there.
Stay on track and keep doing the WC's and dosing 250mg per 10/G.
Only do 100% WC's if the water if getting real funky or cloudy. Otherwise do 50%.
Siphon out all detritus when your doing WC's.
Stay with it, keep taking pics.