Why Do Upflow Scrubbers Need Bubbles?

[Crusinjimbo]

I am curious as to why a waterfall type operates on cascading water but submerged upflow types operate with bubbles. Why doesn't an upflow scrubber run well using a pump to push the requisite volume of water up and accross the screen. I can control the water flow velocity and the "impact" of the water accross the screen by choosing pump capacity and the design of the screen holder. My current upflow is a 1" deep acrylic box (6"w x 10"h) that resides in my sump lit by LEDs through the sump glass. Airstone are a PITA and I want to remove the air pump and drive it with a Rio pump feeding into a plenum that distributes the flow accross the bottom similar to a waterfall type distribution pipe.

[SantaMonica]

Because, a scrubber needs an air/water interface. A waterfall is very thin water, next to air. To do this underwater, needs bubbles.

Yes airstones are a pain, which is why we don't use them. Sliced airline is much better, or even an air manifold.

[mattberrytr]

Has this actually been proven? (the need for exposure to oxygen), there is oxygen present in the water of course anyway. Algae happily grows submerged in the display tank. Could it not be that the algae scrubber simply provides a much better environment for algae to thrive, due to the high flow + good lighting?

[SantaMonica]

CO2, not oxygen; yes

Yes algae grows in a tank, but it does not grow as fast a rate.

Yes the scrubber environment is best for growth.

Try for yourself if you like, underwater with no bubbles. A waterfall has no bubbles, but only grows fast where the air/water interface is very thin.

[mattberrytr]

Yep but I'd say a huge reason algae doesn't grow in the display tank is because of the lighting, completely different than what's in a scrubber. Just like if you used only white/blue led's in an algae scrubber, probably wouldn't work too well.

I think it'd be quite difficult to build an algae scrubber submerged with decent lighting and flow over the mesh screen (using only a water pump) but certainly doable.

I think I'll try it :)

[Crusinjimbo]

Santa Monica, could you please detail a bit of information on "sliced airline" and manifold air feeds? I know I have seen something on airline slicing somewhere but can't immediately locate. Thanks.

[FrozenReef]

The water is going to find the path of least resistance and most of the flow is not going to be in contact with the algae.

[SantaMonica]

The tubing is just cut lengthwise, and with cross-cuts. Here is the old way cut every 1/2 inch:

http://www.santa-monica.cc/zoomify.asp?catalogid=38&image=assets/images/UAS-HOG1-tubing.jpg

Here is the newer way cut every inch:

http://www.santa-monica.cc/zoomify.asp?catalogid=50&image=assets/images/HOG3tubing.jpg

[Aquaman]

I am designing something myself and am contemplating using either a powerhead with an airline inserted to inject air, or simply using the return from my protein skimmer. Does anyone have any experience with doing something like this rather than using an air pump? If not, any educated guesses as to if this could work efficiently?

[SantaMonica]

I think someone has done the skimmer thing before.