Since I have been running my scrubber temporarily on top of a tank, and it sheds light into the tank all night, I have been battling a cyano and dino issue for the last couple of months. I decided to run a canister filter for a few weeks to suck out the cyano after blowing it off the rocks. I let it run for about a week and it was pretty clogged up so I shut it down but couldn't clean it for a day. I did that last night and about lost my lunch when I opened it up. Talk about gross. It stank of spoiled seafood, and I mean STANK. If anyone has smelled it, cyanobacteria has a distinct odor to it, I have found this odor to be exactly that of Anthelia / Waving Hand coral. The odor from the canister filter (a diatom cartridge) was NOT this odor. The filter had effectively removed food from the water column and shutting it down for a day before cleaning allowed it to rot.
It was the second grossest thing I have smelled in a reef tank. The grossest was when I was cleaning a pump on a system that had not been cleaned in a few years - that smelled like I opened a sewer drain.
Algae never smells that bad.