Can you overscrubb?

[tang2]

I have been researching a lot about Algae Scrubbers. Let me say you have been busy Santa Monica! You are definitely getting the word out. Is it possible to over scrub , with too much light and a oversized screen ? Or will the algae growth slow or stop as Phosphates and Nitrates gets close to TRUE zero. Then will the filter will grow at a given rate as needed? Or will it die off and leach back into the water. I have been thinking how to make it the MOST effective. One thing is I want it to run 24 hrs so there is no down time filtering. So Im building two filters and overlapping the time their on, using t-5 lights with horizontal screens.

[SantaMonica]

You cannot over-scrub. As the nutrients fall, there will be less growth. The big difference of a powerful scrubber is what happens when there is a high load: A weak scrubber will not keep up, and nutrients will rise, whereas a powerful scrubber will keep nutrients unmeasurable.

Remember that horizontal screens need 2X the area as vertical screens.

[tang2]

Does that mean if the size of screen for a vertical is 120 square inches, then a horizontal will be 240 ?

[worley]

Yes, and the lights that would have been across two sides would be all on one side. You can however have half the standard flow (17-18gal/hour per inch of width instead of 35) as it's normally split between two sides, but I'd aim for around 20 gal/hour/inch to be safe (of actual flow, rather than pump rating)

[kcress]

Summary of from vertical to horizontal:
Half the flow.
Same light.
Twice the area.

[tang2]

I am confused, I thought by having a horizontal screen it is more effective because the water being filtered doesn't keep flowing down the vertical screen after being removed of nitrates and phosphates. The whole screen is getting unfiltered water running on it. Since the top 5-6 inches is pulling the most out. So why would the screen area need to be doubled if it is more effective. Just to give an example a horizontal screen 24'' wide X 5'' tall would equal 120 square inches. A vertical screen of 5'' wide by 24'' tall would equal 120 square inches. From my understanding of what you guys are saying the horizontal screen would need to be 48' wide' X 5'' tall to equal the 24" tall x 5'' wide screen. Is that right? ( without understanding the mechanics of why ? It is difficult to be good at anything, its nearly impossible to improve upon or to master it! ) Thanks for all the help!

[SantaMonica]

I've got to disagree on the half flow. I think horizontal's need as much flow as possible in order to create the turbulence that's needed to get good growth. High flow is needed, but horizontal's normally have low flow. So putting all 35 gph/in on one side should give it the extra push to move the water over the screen.

[tang2]

More confusion i don't see how a horizontal screen with the same area as a vertical, uses less flow. It will always needs more because it needs to push the water farther to reach to the end of the pipe. With a lot more water being released down the screen at the same time. Santa Monica has stated that in a lot of the blogs. But I have not read about this double the size if its horizontal vs vertical. That one really does not make sense logically maybe the misunderstanding is the meaning of vertical verses horizontal. Can somebody explain WHY they think the horizontal screens need to be twice as big if its more effective ?

[worley]

You've got very confused it seems lol!
Horizontal scrubbers are NOT more effective, if you're lucky they can be as effective.
You need to DOUBLE the area on a horizontal scrubber to get the same effectiveness.

E.g. a 12" x 12" screen that is vertical and lit from both sides would need to be 24"x12" or 12"x24" on the horizontal screen to have the same area (as you're only using one side, on a vertical where you use both sides 12x12 = 144 square inches per side, so 288 square inches total area, on a single sided horizontal scrubber you need a screen twice the size to get the same area).

The reason you can half the flow of water is that on a double sided vertical screen 35 gal/hour per inch goes over BOTH sides of the screen, on a single sided horizontal screen, you only need what goes over one of those sides, therefore half, so 17-18 gal/hour per inch of width.
You can make the screen nearly as long as you want (on either vertical or horizontal) without affecting the flow of water needed, as long as the entire screen gets the required flow (17-18 gal/hour per inch per side).

The usual rule of thumb we use is 1 square inch of screen, lit from both sides per us gal of water volume, therefore 2 square inches lit from one side.
So you should be able to see now that the pipe that attaches to the top of the screen can be the same length but only require half the water flow, as long as the overall area exposed to the light and water is the same and the width is the same (so the physical screen is twice the length of a vertical equivalent on a horizontal setup).

So to sum up, think of the rules as:
18 gal per hour per inch of width per side
(imagine cutting a double sided screen down the middle and folding it out to be a single sided screen, the water flow would still be the same but over twice the width and the same height, or you can do it the other way and double the height and half the flow)
2 square inches of total lit screen area per US gal of water volume under normal fish/food load.
So a double sided screen has twice the area, so if you look at one side it's 1 square inch per US gal as it is lit from both sides

[tang2]

Ah Ha! THANKS Worley. No more confusion. LOL I was assuming we were comparing the same amount of sides of light and screen, wether it was one or two sides. Isn't Santa Monicas acrylic box considered a horizontal screen being 24 X 5. His set up was running lights on both sides. I was using this set up as my reference. Once again thanks for answering my redundant questions. Like I tell my wife don't ever assume if you want the right answer.lol

[farmhand]

I've got to disagree on the half flow. I think horizontal's need as much flow as possible in order to create the turbulence that's needed to get good growth. High flow is needed, but horizontal's normally have low flow. So putting all 35 gph/in on one side should give it the extra push to move the water over the screen.

Do you know that turbulence (assuming more oxygen) helps algae grow faster? If you designed a horizontal pan say 1/2" deep with slow moving water and lights above, would it grow algae just as fast?

[SantaMonica]

It would not grow at all.

Turf algae are the types that grow at the surface/shore, or slightly below, where there is a lot of movement and mixing with air. Some turf can survive in air and full sun for hours.

[worley]

Yeah, I guess my calculations for a single sided are probably off, my scrubber isn't exactly horizontal, it's at a 30 degree slope. However, I do myself have nearly double that flow, and I've been getting good results. Just did a clean yesterday and the entire screen has a fairly thick layer of really dense carpeted turf algae that I have to scrape fairly hard to get off with a plastic card, coming off in large carpet-like chunks =)