More like find where detritus is accumulating and get rid of it; a power head with or w/o a piece of vinyl tubing, or a turkey baster is great to dislodge wastes that settled in the rocks even if you have outstanding random flow. The sand bed is suspect. Are you using socks and cleaning them enough, how grungy has the sump or fuge become? It may turn out there isn't a lot of waste stored in those places and a GAC and GFO routine could get the tank over the hump. Maybe doing better more routine water changes with very low or 0 tds will take care of it; I feel wc's are more than letting a few gallons out and replacing them, rather it's when I get in somewhere with a vacuum or syphon hose and find some gunk. Remember it's taken awhile to get to this point and it should take a will to get back to where you want it.