found this helpful post made by one of the form moderators ...
"That is cyano in the beginning stages,
Improving water quality (with lower nutrients)is a main step - leaving the algae with less fuel for growth. With PO4 & NO3 at zero you may still find cyano.(as many ppl have)
This is because Rocks and sand(substrate) act as a sink. Cyano will grow over these surfaces until that runs out then die off by itself. All this while the water should have low nutrients(or very very low levels,near zero) so that the algae has nothing else to use up and will go away in a few weeks to a month or two.
For a new tank- there is no way you can avoid the first cyano outbreak (it may come in the first month or in the first year).
Siphoning off whatever you can helps keep it in small patches, but you have to keep doing it till it goes away. If water changes are done during this time- the new water should be nutrient free too- or you fuel the cyano."
IMO, cyano is part & parcel of life. Looking after your water will stop future outbreaks.
If you use red slime, becareful of low oxygen levels. Increase aeration or water circulation during treatment.