There seems to be quite a lot of questions about algae on all forums I attend just lately as always it is a bad point with many people. Personally I like some algae in my tanks to give a more natural look and feel to the tanks. Those that don’t like and want to rid algae in a tropical tank with or with out plants, can use the blackout (BO) method. BO does NOT cure the underlying problem that has caused the algae bloom in the first place but mealy re-sets the tank conditions back to as near normal as possible. Depending on the severity of the algae bloom a BO can be from 3 days to 5 days.
1. Feed the fish about 1hr before starting the blackout (BO) then do a 50% water change. 2. Turn off c02 if you use it and install an air stone. If you don’t have an air stone to Airriate the water then adjust the filter so it moves the surface of the water as much as possible. 3. Completely cover the tank in the darkest sheets you have or double layers of black bin bags to block out ALL light. 4. Leave the tank fully covered for 5 days. YES fully covered for 5 days. DO NOT PEEP. DO NOT FEED THE FISH. I must admit I did peep half way through a BO just to check all the fish and that there were no problems in the tank, and then recovered till the end of the 5 days. DO NOT FEED. 5. At the end of the BO DO NOT remove all covers at once but slowly remove the covers over approx half an hour so as not to blind the fish with excess light. Do a 50% water change and lightly feed the fish. Remove air stone and restart c02 if it is used.
After doing the BO depending on the type of algae you had you may find the filter might be running a bit slower than normal if the algae has blocked the filter. If this is the case DO NOT strip the filter down as the tank is already a bit unbalanced due to the slowing of the plants during the blackout and the dieing algae. You need to have a stable bio-film to process any ammonia issues quickly. With an extensive cleaning of your filter you will more than likely remove a huge portion of the bio-film and bio-filtering capacity. The blackout method does work, I know by experience, in most tropical and planted tanks with community fish. If you have sensitive fish I would strongly advise to seek advice before doing a BO. The only problem I know of at this time doing a BO is that some of the more delicate plants may suffer as will all plants having no light. Most will be leggy after the BO as they have been searching for any light. This should pass and within a week should be back to near normal.