As I was saying, I got a dragon gobi to work on my substrate. It seems that after about 15 years of use, the sand-bed had become too full of debris that was decaying at a rate fast enough to feed the Cyanobacteria, but not enough to pollute the water. I say this because all parameters were good, filter bags/socks relatively clean, and all looked well.
The fist thing the Dragon Gobi after acclimation was to start eating Cyano by the mouthful as he filtered and released the cleaned substrate, along with a wisp of silt that would float off. I had no idea this fish would eat cyano, and it turns out he wasn’t really eating it at all. He was feeding on the sand just below the cyano where it was richest in nutrients and critters I suppose, and had to sift the surface first. I watched him for a while before lights out. He seemed quite busy “tilling the soil”.
When I got up the next day, it looked like there was a scirocco, or sandstorm in the tank. Those little wisps of silt add up quick when it is constant like this all night. Also, the little guy had toppled over a set of soccer ball sized rocks that were stacked vertically on top each other. He apparently kept burrowing through the night to do this by removing the supporting substrate. Watch out for this if you get one of these fish, as the rock could have fallen forward into the glass. Tall structures may tumble if not supported well.
After a few days there is no sign of cyanobacteria, the tank is in great shape, but the overflow bags are getting really dark with dirty silty stuff. They need changing daily now. Corals and live rocks are being blown down with a turkey baster until things calm down. I will have to update on how he works out in the long run. I have not seen him eat any other fish foods yet. He does nip at freeze-dried krill, but ignores frozen foods so far, even cyclopeeze. I think he is just getting the pods, as I can see him pick on the rocks occasionally now . After about a week he has plowed my entire tank and the substrate never looked better.