Green, red, brown? I've cleaned my sump before without issue or should I say it didn't it make my display any worse than it was. My current/past situation was Cyano. That passed after about a years worth trying the chems that didn't work. I didn't try too hard. It was ugly but bearable. Algae doesn't really bother me too much like others. I am absolutely positively convinced that flow isn't a contibutor to Cyano. Why is always Cyano and not another or a combo of algaes? Then there was very short green hair looking algae. Like a fuzz. Again not bad. That too passed recently and my tank is looking better than ever. My acrylic grows algae almost over night though while rock and sand remains amazingly clean.
I swapped out rock from my sump to Chaeto about a month or so ago as well as using "Dr. Tims Waste Away" on a weekly basis. Which one or is it a combo of all? Or after a couple of years or better it's settling in and becoming balanced? I will note my sump is also growing a good film of green algae in the fuge area. So is it the Chaeto or green slime? Makes me ponder a Scrubber. Planning on a tank swap and holding off because of the current one looking so good.Trials of the hobby.
I say hold off and see what develops. Maybe a new fish like a Dragon Goby. My Lawnmower blenny does wonders on rock, acrylic and sifts sand.. Then we are going through a weather change. Whats you water temp?