1) How often do you do water changes? Do you use RO/DI or tap water?
2) What are your nitrate/nitrite levels?
3) How long do you leave lights on in tank? What kelvin/type of lights?
4) Is there direct sunlight in the tank?
5) Do you have snails/crabs/algae pack in you tank?
6) Do you have a sump/refugem?

1) Once per month - 25l of RO for my 200-250L tank.
2) 0
3) 8 hours per day (we are now in winter) 4 x T5's (one blue 3 white).
4) Nope
5) Nope but I do have a phosphate remover running in my Fluval filter.
6) Yes I do.

Is this just as it is a new tank? What am I doing wrong?


Try this way :

Do not brush the algae. Wait and it should gone by itselfe. If the
parameters of water and other stuff are OK, it will not come back