Cyano makes its own food and does not need light, cyano gets its food by taking N directly from the decaying matter, cyano is bacteria.
I respectfully disagree, KcMopar. Cyanobacteria needs light, nitrogen, and phosphorus to live. This website explains how they live and spread.
http://www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/cyanobacter-eng.php
Or is it advisable to just do a blackout for a week? I'd rather make sure 100% it's gone, I can do any and all necessary maintenance.
Dan - If you are willing to do the necessary water changes, this is what my Ecology class did for a class experiment at a community college.
We had 4 different aquariums, identical in light, bioload, plant mass (floating plants and stem plants with weights to keep them submerged) and no gravel. They were 20 gallons each and deliberately infected with the same cyanobacteria 14 days before the experiments started.
Tank 1: Antibiotics were used and 25% water changes done daily.
Tank 2: 50% water changes, 2 times per day.
Tank 3: Antibiotics and Blackout for 7 days, no water changes.
Tank 4: Blackout for 7 days, with 25% daily water changes.
All fish were fed daily with sinking pellets. All had the same hang-on-the-back filter and it was kept running for the duration of the experiment. All tanks were cycled and had been running for about 8 months.
For Tanks 3 and 4, to prevent any light from coming in, the blackout was not removed at all (thick black blanket wrapped around tank, including taping it to prevent any light from getting in. We left one corner with a flap so we could drop the food in. We'd put our hand under the flap, feel for the edge of the water and drop in the food. This prevented any light from reaching inside.
For Tank 4, we had a 5 gallon bucket sitting on a counter above the tank level with a piece of airline tubing leading into the tank, in a similar 'flap' fashion as the 'pellet flap'. To do water changes on this tank, we'd lower the bucket to the floor, start the syphon and drain out 5 gallons of water. When we had the bucket full, we'd 'pinch' the air line tubing to prevent further syphoning, empty the bucket, fill it with clean water and dechlorinate it. Then we'd put the bucket on the counter above tank level, 'unpinch' the tubing while underwater in the bucket, which would automatically restart the syphon.
At the end of day 7, the experiment stopped. We cleaned each tank of all visible cyano (dead or alive) with seperate equipment so not to cross contaminate things.
Only Tank 4 was completely 100% free of cyano. From day 8 to 30 (the end of the class), no cyano was ever seen in that tank. No loss of fish, plants were a bit droopy after no light for 7 days, but they all recovered.
The 'cycle' of the Tanks 1, 2, and 4 were not affected. Tank 3, the cycle was destroyed. We concluded that it was the combo of the antibiotics and decaying of the cyano that caused the beneficial bacteria die off.
