Grey algae??

My 65g tank (EI, CO2) has been find for months -- sort of. When I was on vacation in the summer (9 days) algae, thread and BBA mostly, got out of control and I have been fighting to hold it in check until I get a few days in a row when I want to move the fish to a bare 30g I have, and do a complete rebuild of the tank.

HOWEVER, this morning (in a period of about 6 hours), it developed what I first thought was grey water. On closer inspection, the sides of the tank (inside the glass) were coated in what I looked like tiny threads of grey. May not have been threads, scraping brought off small sheets of grey material -- and before that some of this material was floating in the water. My filter (a bio-wheel with those flat rectangular cartridges) had a huge buildup on it, was very heavy when I removed it, just replaced it 5 days ago. I replaced the filter.

Not sure what this is, any thoughts for me?? Fish look happy enough. No testing done yet, will do a bit -- ammonia, nitrite -- don't expect to find anything though.

edit: DID find something -- Nitrite is off the scale. Ammonia is 0, ph is 6.4 (normal for me), nitrate is 40 -- so everything is fine except the nitrite. I found my biowheel was not turning, but it was wet -- I think it go heavy with the load of grey matter -- I rinsed it in tank water and its turning again, I don't think this was the cause. I don't see any fish missing.

 

This was NOT algae -- some kind of bacterial bloom.

I changed 75% of the water this morning, by the time I got home from work I had lost 4 bala sharks, 4 shrimp (so far) and 3 head and tail lights.

In desparation, I will move the rest through 2 baths into my 30g tank for
now.

I will build my 65g from scratch -- the 30g should be OK for now -- may add
some extra air.