Submerged, rotating cylinder algae scrubber (with video)

2nd Week update:

Algae growth looking good on the patches it previously grew in, and looks like it's starting to grow in between. No whiting like last time, so it's looking more promising this time with the lower flow.

 

Yesterday I increased the intensity to 70% and the duration to 15 hours.
Checked today and it's looking good, I'm seeing a bit more growth each day.

 

Third week update:
Phosphate: 0.37ppm
Nitrate: 40ppm

Growth looking good. Upped the LEDs to 100% intensity today, duration still at 15 hours.

 

Forgot to mention that on I discovered Sunday morning that the return pump for this tank (Jebao DC1200) died on me, so I had to use my Eheim 1000 (which was connected to this scrubber) as the return pump, and I connected my Eheim 600 pump to the scrubber. I dropped the flow rate/head pressure down so the screen is rotating at ~90 RPM, which is around the speed it had been rotating at over the last three weeks, when paired with the Eheim 1000.

One concern I've always had with this scrubber design is the potential for the weight of the algae growth to slow down the rotation of the screen, and possibly it stopping from rotating completely, so today I decided to do some tests.

I measured the rotation of the scrubber with and without the algae growth cylinder. I did each test twice.
Where it's just the acrylic rod rotating (no 3d printed cylinder and algae screen), it took 40 seconds the first time, and 41 the second time for the screen to fully rotate 60 times.
When the 3d printed screen with the algae growth was added, it took 43 seconds both times to fully rotate 60 times.
I'd estimate the weight of the 3d printed screen and algae growth to be about 100 grams, so the additional weight and water resistance hasn't had as much of an impact as what I thought it might. Will be interesting to see the impact on the rotation as the growth gets thicker.

 

Gave the screen a clean today, and dropped the intensity back down to 70%. Most of the growth was green dense algae, not long hair algae. Hopefully I'll start to see some more of the standard hair algae growing on the screen.

 

Fourth week update:
Growth has been OK, but not great been great since I cleaned it on Wednesday, so won't bother with the tank parameters. The dense, thin growth seems to have no problem growing, but very little of the typical GHA. There is some GHA looking growth at the top of the screen (top left of pic). The very top of the scrubber/screen is pretty much sitting on the water line, so that aspect could possibly be causing this type of growth. I was hoping for this type of growth over the whole screen...I guess it's only been up and running a month but still, it's disappointing. Today I dropped the LED intensity back down to 50%, just in case the LEDs are too intense (hence GHA at the top, an area of slightly less intensity). The flow could also still be too high, ideally I'd like to stop and start the screen, or slow it right down, then speed it up, similar to a surge scrubber. Bubbles collect on the screen as well, it's hard to know the impact of this, but it could be an issue. I tried dropping the flow down even further, but I risk the screen stopping completely.

I think I need to build another version, capable of detecting the RPM of the screen, and automatically adjusting the pump to match the desired rotation speed. It'll also let me test out a stop/start or normal/slow rotation speed, to try and imitate surge scrubbers. That's what I'm working on now, hopefully it'll help to clarify if I'm wasting my time with this and need to move on to something else, or if there is potential in this design.

 

I lowered intensity to rule out hair algae not being able to grow because of too might light. There's a reasonable sized patch of GHA looking growth at the top of the screen, as well as a smaller amount at the bottom of it. There's a bit less light at the very top and bottom of the screen, so I thought that may be a factor in why the GHA has started growing there, but nowhere else.

 

Fifth week update:
The GHA seems to grow well but it's only on a few small portions of the screen, it's slowly spreading though. The dense thin growth has again died back on portions of the screen. I think it's a flow issue (still too much), but there's no way to tell for sure, as if I slow the speed down too much the screen can stop, and won't start again by itself. So, am going to do some testing in the next week or two, by having a DC pump control the flow. I'll probably set it to cycle on and off every 20 seconds, i.e. spin for 20, off for 20.

Am also working on a proper surge scrubber, no too dissimilar in functionality to my surge model from almost a year ago. The design for that is almost finished, so I should have that up and running in the next week or two as well. The two scrubbers can then duke it out to see what method is superior.

 

Odd bare patch

 

Yeah the lighting is only at 50%. I'll bump it up now. The growth is even all over, so why would that patch die off, and not the whole thing? There's a tonne of pods on the screen, could it be caused by them? I only seem to have this problem on that dense thin specific type of growth, there's quite a bit of GHA on the top of the screen which is growing well. It's popping up on other areas of the screen as well, so I think in time it'll take over, hopefully anyway.

 

Sixth week update:
Looks similar to the previously posted pic.
Will have a new version up and running soon which operates differently to this version.

 

Seventh week update:
Gave the screen a clean a couple of days ago, the GHA is slowly popping up over the screen and replacing the dense thin growth.
New version scrubber should be up and running in the next couple of days all going well.

 

Hadn't thought about using mirrored acrylic, it sounds like it would work great. I don't think I would go down that path with this scrubber though, as I don't think the benefits would outweigh the added labour time. I'd probably just add another LED or two if I found I needed more light. Since the algae cylinder is rotating at a pretty fast speed, the entire surface of the screen is getting hit with high intensity light as it passes past the LEDs. I did think about using acrylic that is black on one side, and white on the other. I'm pretty sure that exists if I remember correctly. The white would face inside the scrubber, and would reflect a lot more light around inside the box compared to a black interior.