New Santa Monica RAIN2 Algae Scrubber

That growth looks a ton better than the last few sets of pics. You're doing it right, I'm assuming that you rinse out the screen after scraping under tap water for a while also?

 

Orange circles could be areas that grew thick enough to block light and then there was a bit of detachment, so the orange is kind of like where the growth is starting over, not 100% sure that's what it is but that is my guess

Honestly I'm not a big fan of the 3D printed screens. I haven't tried one myself but I've seen & felt them. I'm just not sold on them being the best material, but I don't think that's necessarily the cause of any of the issues you're having getting the screen going. The orange spots, maybe. From what I saw with the 3D printed screen I looked at (it was a long time ago and I didn't look at it under a microscope) it seems like any 3D printed material has a smoothness to it that is inherent to the way 3D printing works, while at the same time it has pores, but I would expect that at a microscopic level, even the pores are smooth.

I'm still actually trying to find a better screen material, the plastic canvas has sort of the same issue - even when you rough it up, it's still a bunch of shredded up smooth plastic, but the algae does seem to anchor to it well over time, so this might be the same thing with the 3D printed screens - over time, they are fine. So I have refrained from slamming on them as I have no solid basis to poo-poo them completely.

When Paul Baldassano (Paul B on R2R) posted about making the mortar screen, that's when I dove in and started making those. It's a simple solution and it works very well - the mortar, once cured, is extremely rough and porous, so algae attaches to it easily relative to any other material I've tried. Plus it's super cheap and simple.

 

I'm honestly a bit perplexed, it looks like the screen is bare in that area where the orange used to be. Is this pic after you scrubbed the growth off?

 

Iron is highly reactive and nearly impossible to sustain at measurable levels in a reef tank. SM did an experiment once to see how much iron he could dose a 90g tank before it essentially killed everything in the tank. That turned out, IIRC, to be about 1/2 gallon in one shot.

I believe it was Kent Iron & Manganese he was dosing but I could be wrong about that. People will also buy iron supplements and crush them up and dissolve them to dose iron. I can't remember the exact brand but that does matter, Fe++ or something like that. I might have a thread here about it

 

Here:

Dripping Potassium & Iron

 

No, I'm saying the test is not really relevant since Iron gets depleted fast. You can add it, it should boost algae growth which might give the scrubber a bit of a kick-start. But it's difficult to say if that kick-start will continue after you stop dosing.