VaughnH;34667 said:It looks like blue green algae, cyanobacteria, which tends to show up where there is high light and a shortage of nitrates. When I have had it it is usually at the water-substrate line or below, and where the sunlight hits the tank. I'm not an algae expert, so I fully expect to be wrong here, but that's what it looks like to me.
Here is a link to algae id and some tips and remedies:
Aquarium Algae ID (updated 16th Spet '08)
If it is cyno, try reducing your light, increase your N dosing, and I have also had issues with BGA when my c02 was not right...........
Also ensure that filter maintenance is up to snuff..........
wilsar;35650 said:i have found that manual removal to be affective , using a small diameter air hose to carefully syphon BGA from the substrate/plants every two days for as long as it takes until the tank stabilizes and the plants begin to show signs of growth. i have had cyano outbreak in only a few tanks(start ups), even though i use the same substrate/lights/dosing in all my tanks. cyano seems to favour the tanks that are planted with slow growing plants and i have noticed my tanks with Vallisneria tend to skip this malady, maybe because Vallisneria has the ability to release nutrients back into the water column.