one question is why is the water in the sump so high?

Mine is located behind my tank with ZERO way of getting it out but it is crystal clear. I clean mine in place with less room then you have. Just use a gravel vac's hose to clean it out, then a towel to wipe it down inside the sump.

Carbon if not maintained will leech toxic crap back into the tank. new bio balls and new filter pads are great, might want to get a new sponge for the sump itself(seperates the bio area from the pump area.