I've been unhappy with the slot design on my scrubber. It's always been a bit finicky and prone to getting growth up in it. After I switched to Herbie style drains, that meant that it would throw off the balance of the drains and send water down the backup drains as the algae grew. I tried several light blocking schemes, but they didn't seem to fix the problem. Since the slot would get gummed up after a week or so, I could never let the scrubber really grow to the "3D" stage.
The current solution to the problem, which I have only run now for two weeks, so it is still "experimental", does away with the slot altogether. To hang the screen, I made a "loop" of plastic canvas, and stitched that to the top of the screen with braided fishing line. The screen then hangs from the pipe by the loop, and the pipe just slides into the loop. No need for zip ties or curtain rings to hold a screen in a slot. For flow, I drilled a 3/16" hole every 1/2" along the pipe. The holes point down. The water flows out of the holes into the area where the loop joins the screen, then through the holes in the plastic canvas loop and down either side of the screen. The flow is very even along the screen.
For reference, the scrubber box is roughly 20" long by 10" high. I added an extension to the box so the pipe actually sits up above the box by an inch. The pipe is 3/4", about 20" long. Flow comes in from both ends. Roughly 800-900 gph of total flow. There are two screens, each roughly 10" by 10". The scrubber is LED lit. See one of my other threads for details on the LEDs.
Have a look at the pictures. Maybe that will help my explanation...
I did get some spray where the loop joined the screen, since the pipe sits above the box, that would have killed the solution, but then something Floyd mentioned in one of his posts caught my attention... Saranwrap. I laid a piece of Saranwrap over the loop and stopped the spray immediately. The drag created by the flow pulls the plastic wrap right down to the screen, but it doesn't stop the flow, it just evens it out a bit. Then, I wondered if a piece of thin plastic from a black plastic garbage bag would do the job, since it would also be a great light blocker as well. I tried it and it worked like a charm.
I'm extremely pleased with how the new setup is working-- no spray, no growth into the slot messing up the flow, perfectly even flow across the screen. I let it go for two weeks and just about filled up the box with algae.
If you are having trouble with the slot-- cutting it, getting it the right width, keeping it clean, etc., give some thought to trying this system. Even if you stick with the slot, try the garbage bag light blocker, I think you'll be pleased with what it does for evening the flow.
Pic1-- screen hanging from the pipe by the loop
Pic2-- the pipe with the holes
Pic3-- screen hanging in the box
Pic4-- with the black plastic as a spray guard
Note on the screen on the left side in Pic2-- this is a new screen, but I stitched pieces of an old screen to it to seed it. I'll let it run this way for another couple weeks, then take the old pieces off.