green spot algae


Junior Poster
Jan 25, 2009
Mitchell, Ont
I have lots of green spot algae on my 55 gallon tank, what is this tank lacking.... I currently dose with seachem fertilizers according to there chart for a 55 gallon. It is heavy planted....pressurized c02..etc.
I heard greeen spot algae was a lack of phosphates, should I be dosing more phospates, and then I also read it was a lack of potassium..Confussed..

Lighting, is 2x 54 wt t5 high output lighting , with lighting on for 5 hrs off for 2 hrs, and on for anohter 5 hours, with total 10 hrs daily... any help would be appreciated..


Lifetime Charter Member
Lifetime Member
Nov 21, 2007
Los Angeles, CA
Below is an excerpt from: Aquarium Algae ID (updated 16th Spet '08)

Green Spot Algae prefer direct light. It forms green spots on aquarium glass and slow growing plants that are exposed to strong light. This algae will appear if CO2 and Phosphate (PO4) levels are low. Since it is very hard, algae eaters can't do much in eliminating this algae. Neritina Zebra snail is the only algae eater known that can, literally, eradicate the Green Spot Algae. It can be scraped manually off of the glass with a razor blade. In a case of an acrylic aquarium use plastic razors only. This algae is considered normal in small amounts.
To prevent this algae keep stable CO2 levels, dose NPK regularly and improve the water circulation throughout the tank for better nutrient transport. Keep slow growing plants in places where they will get less light.

I've had some GSA up high on my aquarium glass in pretty much all of my tanks -- both CO2 and non-CO2. Also, if I put anubias in a higher light area, they will get some on their leaves. But, I got some Nerite snails (as mentioned in the above article), they totally wipe this stuff out ... both from the glass and the anubias (I have since learned to put anubias in darker areas). I think also that some plecos will take this stuff off of glass -- maybe rubber noses, but I'm not sure.