Cyanobacteria

[SCMurphy]

Use the erythromicine for about twice as long as you have been, and try spot killing with a little (key word is little) hydrogen peroxcide. Do a water change about 30 minutes after using the hp so that you don't harm any fauna.

[150EH]

I have this algae again in my 150 and my 10 gallon tanks, with the ten gallon being a fairly new tank it has none of the suggested symptoms of the link listed by Cristy, just above but the 150 does have a build up of organics if dead plant matter counts. I'm going to try the above treatment again as it always seems to work but then I'll have a recurrence after a few months, so I want to alter it in some fashion without going overboard with my good nitrifying bacteria being my only worry. I was thinking about adding an extra day of 2.5 mg/l of Maracyn on day 5 and then increasing the final dosage to this same amount as an extra punch to keep it from coming back, do you think this will work?

So far my luck with livestock staying alive with this method has been good so I don't want to change from Maracyn, plus I already have enough on hand to treat both tanks.

[tug]

Did you try adding a powerhead and directing it towards the problem area?
If it is localized it can be a circulation issue.

Whatever is causing the outbreak, your dissolved organic carbon (DOC) level is most likely high. Yes, dead plant matter counts.

Rich substrates without enough plant growth can also contribute to an outbreak, particularly in young tanks. ADA As seems to have a higher incidence of BGA than plain sand/commercial inert sediments but is found in older plain sand sediments as well. Potassium permanganate is not a cure as such for cyanobacteria, but can go a long way toward reducing the underlying problem of high dissolved organic material.

I do not know enough about your planted tank but if you stopped dosing KNO3 for awhile, BGA will rear it's ugly head. Basically the question to ask: what is causing sub optimal plant growth?

I think that BGA is caused by several different combinations of stimuli, working together. For example too much light in combination with insufficient nutrients and hard water might cause it.

Or, too little light together with a high DOC might be a cause, etc.

Try to up the biological filtration/improving O2 levels and focus on good plant growth, removing dead plant mater to lower the tanks biological oxygen demand.