New to scrubbers diy

I need a frame of reference on the overall system. How old is it (i.e. history of not only the system but the rocks, etc), how much do you feed, what is livestock, your past husbandry, nutrient levels, etc.

 

Thanks for that. That is a relatively high bioload, so you're good on the size and lighting I think.

The screen looks like it's still generating a lot of slime. This can be a phase that the scrubber goes through as the "set point" of the tank shifts. Algae and slime in the tank are "opportunistic", so they thrive on imbalance. If you've been running biopellets and rowaphos for a long time, then you take them out completely all at once, this can "shock" the system and result in unwanted algae. Your bacterial population and composition is used to one set of conditions, and when you change that (even by flipping rocks over) there is a mini-cycle that occurs as the bacteria re-adjust and try to find a new balance point. This is why it's important to make changes slowly.

The presence of a more powerful/efficient scrubber may also be causing a change in water chemistry that results in nutrients coming out of the rocks versus entering into them, and the combination of nutrients, water flow, and light at the rock surface can result in algae growth there for a period of time. This can last as long as 6 months, depending on the condition of your rock (hopefully not that long).

What I would do at this point is take the screen out at least 2x per week and swipe your palm across it and rinse it off to get rid of the slime, but leave all the GHA behind. This should be a 1-2 minute operation, no scrubbing, no scraping. This helps to prevent slime buildup, which tends to inhibit GHA growth. Your GHA is there, you can see it, but it's covered up with the slime which is slowing it down. You might need to follow this regimen for a while, it depends on your system. You might be able to back off to once every 5 days eventually, judge it as you go.

Harvests: no scraping, or only scrape 50% of the GHA off. Do this every 10-14 days, but no sooner than 10 days between harvests (longer if you can, as long as there is no detachment)

Light intensity: you can increase it. I think you said 40%, bump to 50%. I usually tell people to start at 9-12 hrs/day and 25% intensity for 2-4 weeks (until a base of growth forms) and then alternate adding hours and intensity once every 7-14 days until you get to 18 hrs/day and 50% intensity, then hold for 2 harvests. Then start adding hours again until you get to 22, then start adding intensity. Running 24/7 is OK, but you have to watch the intensity as this is the "instantaneous" factor, and can result in a reversal of growth if the intensity gets too high and your flow and nutrients are not adequate to support the algae growth. I think you're OK, but you will want to make sure you get consistent GHA growth before you go much past 50-60% intensity when running at 24/7

Flow: have you measured the actual flow passing across the screen?