I have changed the water 2 days ago and I haven't dosed the fertilizers yet. Maybe, using Excel, the 1,5 wpg aren't enough. I could add another T5 to bring the wpg up to 2,3. What do you thing? Maybe there has been too much excel/fertilisers and too little lighting.
here is a picture of the algae I see growing on some little stones all over the tank: Attachment 2920