I get pretty similar looking algae on my screen, but sometimes there are brown colors in it with thick gritty clumps. This is the screen. I clean 80% of it every 10 days during water changes and run those cheap amazon lights 12 hrs/day. Doesn't grow much on the back side of the screen but still functions well. The weirdest part is it actually smells good, kinda like a really clean beach.
Hi SamiTANKS;
Is the screen illuminated on the "back side of the screen" ? How's the flow on the backside?
"cheap amazon lights " will grow algae, but not optimally if the intensity is too high or too low, & it will not necessarily grow optimally if the correct spectrum of red light is not provided. These aspects are important for efficient filtration.
Too much blue & not enough red at 660 nm can result in brownish slimey growth, & the slimey brown growth is not good for filtration.
Phosphate assimilation is limited of course if other necessary elements needed for photosynthesis are limited, especially nitrogen.
Your personal experience in regards to phosphate assimilation should not be considered as typical unless your growth is optimal. Your "phosphate also initially dropped to 0" so your algae growth must have been close to optimal at that stage. Perhaps the lights you use have degraded?
cheers