Any experts out there on dealing with Cyanobacteria

[bluelagoon]

IMO, you have an imbalance of CO2 plus a build up of what ever you've been putting in the tank. After all you're leaving 75-80% of the old water in the tank each time you do a WC. This may not be the only cause but when CO2 is used in most tanks you'll need fast growing stem plants that take up nutrients. Some plants do better with increased ferts when CO2 is added, but that's in a well lit, lush green planted tank. The barometric air pressure will put enough CO2 in your tank for those slow growing plants, just like it puts O2 in your tank. I have those plants doing well in non CO2 tanks. Also, I take it that your CO2 is turned off about an hour before the lights go out and not left on all night. I'm thinking a lot of fish means frequent larger WC's too because of the high amount of food going in to feed all those fish. Did you have any issues resolving the last years bloom? How was that resolved?

[Branch]

Things have eased slightly with 40% - 50% W/Cs this week, nothing other than food goes into the tank. I'm away for 2 weeks now so I've turned the C02 off, reduced the lighting duration plus my deputy fish keeper will feed less as not daily W/Cs. I'll reassess when I get back. C02 usually runs 24/7 as it's not dosed excessively and PH is stable at the current level (6.5). Resolved it last year but after a couple of 4 blackouts which, given that this tank has juveniles in that need feeding 3/4 times a day, isn't suitable this time round, at least not until I've grown them out. Will report back when I return from vacation. Thanks for your input.