In my opinion you have a glorified wetland. If you want a decent fishery get rid of the carp and goldfish. They will degrade the water quality ruin conditions for most of the other sport fish species especially trout. Bite the bullet, drain it, clean out all the muck and black slop. Then restart with a clean pond pond basin and fresh conditions. As long as all the muck is in there and carp to stir the bottom the pond will never reach even close to its potential.