thanks!

I indeed add KNO3 and kH2PO4.

I guess I forgot one important detail... Before the change of pH and PO4 I had fuzz algae on the glass everywhere. So it is actual a big improvement! (in my opion anyway). However, I didn´t cleanup my filter, so the current was the same "as always". And still I see a decrease in algae growth on the left side. Thus, I don´t think it is just the current. From your answer about the PO4 level I think I can conclude that the decrease of algae growth is due to the increase in PO4.

greets,

yme