[Narayanan]

How to get rid of it

 

[Yo-han]

Had this in a customers tank too. It was a very clean but for the plants nutrients deprived tank. I fixed it by removed most and increasing fertilization (especially NO3 and PO4).

 

[neilshieh]

Second picture shows blue green algae (it can take the usual blue green color or a reddish brown color as well). The last time I dealt with it I tried all the organic methods (blackout, constant removal, etc.) to no avail and eventually bought maracyn and just dosed it half strength and it was gone in a few days with no ill effects to my filter or shrimp colony. It's typically associated with low nitrate levels and bad water flow + your params being unbalanced in general. You can go ahead and try the organic methods to try to eradicate it but ymmv. Unfortunately they don't sell maracyn anymore but I'm sure you can find euthromycin in other forms elsewhere.