I'd turn off the powerheads, break out the toothbrush, and scrub it clean. Then follow up with a 20-50% water change. Target the stuff you just scrubbed out with the syphon. High water flow (10-20 times the tank volume per hour) will also help with this problem.
Normally I'd recommend adding a natural clean up crew, but with the inhabitants you have they would likely just turn into an expensive meal. A powder brown tang, rabbit fish or any other surgeonfish with a similar body plan will usually help keep it in check, but typically won't mess with the long stuff. They like the lawn mowed first so to speak. Also make sure you have good air contact particularly on the water surface. If there's surface scum, that won't cut it.
Good Luck!