Waterfall scrubbers

[tomahawkins]

Hi,

I'm new to the hobby. My son and I are just starting to cycle our first saltwater tank and we are thinking about building an algae scrubber.

Perhaps this is a naive question, but why does a waterfall configuration promote algae growth? Does algae grow better when it's exposed to the air? Or is it the thin water layer with high flow rate that does it? It seems like a lot of design effort has gone into ensuring the screens receive a smooth continuous flow. What is the theory behind this?

With a saltwater tank, I'm a bit concerned that a waterfall scrubber would loose a lot of water to evaporation. I'm wondering why not just submerge the screen in a thin waterproof box and then pump water through it? Given all else being equal (screen surface area, lighting, flow rate, etc.), how would the performance of a flooded box compare with that of a waterfall configuration?

Thanks!

-Tom

[SantaMonica]

Welcome.

Algae growth on any surface is a combination of flow X light X attachment. A scrubber maximizes these. Also, the air/water interface allows nutrients to get to the algal surface (see pic).

Yes waterfalls do evaporate a lot, although you can enclose them to reduce it. Or you can do an upflow instead, which has no evaporation that I've been able to detect.

The flooded box you mention won't grow hardly at all, because there is no air/water interface. You can prove it to yourself by putting a waterfall or upflow on only part of the box; the part with the turbulence will grow, and the other part won't.

http://www.algaescrubber.net/WhyBubbles.jpg