RFC: Algae scrubber/refugium/gas exchange

[smidoid]

After some scribbling, here's my second attempt at a refugium with an additional gas exchange unit - or algae scrubber built in. The first one works a treat but lacks the gas exchange unit - which I have yet to perfect. This design is part theory, part applied experience - hence it's an RFC (or request for comments) of sorts. I'm building the B section as an addition to the existing refugium when the wife's not looking!

Here's how it works:

Water is fed (by gravity) into the buffer area A. This doesn't need to be too deep - just sufficient to cause the water to flow over the whole length of the weir. It's important that this bit is square and that the whole contraption is level for it to work efficiently. A large particulate filter would be useful here if you don't already have one.

Water drains over the weir onto the glass where it flows over and drops from plate to plate (the exact number isn't crucial - more is better but the law of diminishing returns applies).

This has the effect of increasing the surface area of the complete unit - in theory - by the total surface area of the gass plates. In practice it will be much less than that. Currents created here will cause a gas exhange will allow for algae growth.

There are two distinct ways to build this section.

(1) As a gas-exchange: it can be made into a solid unit - the glass pates can be replaced with acyrilc - or some other waterproof, intert and SMOOTH material. The entire unit or section should be as light-tight as possible to prevent algae growth on the plates since they would be difficult or impossible to clean. Some aerobic bacteria are to be expected but at the expected flow rates these should not pose a problem.

(2) An alage scrubber. This is more complex since the plates have to rail mounted (90 degree angled plastic?) so that they can be removed if necessary for cleaning. Glass or 4mm acrylic would be required here and the entire assembly should be as open to light as possible. (I've used Grow-Lux flourescents in the past and found them effective on freshwater plants). Light should be trained sideways on - lighting this unit from the top will cause algal growth on the upper plates, starving the lower levels of light.

The basic angle of drop for the plates is one I'd like to discuss. A shallow angle slows the water too much; to steep and you lose the benefit of the "folded" design.

Water finally drains into the sump area (C) which can be left empty, but could contain live rock. The final plate can either feed directly into the sump water or drop the flow from a few inches to partially increase aeration (however, this might also cause a scum to from similar to the skimmer action).

From here the buffer glass allows the current to underflow and overflow into the live sand section (D). It's important that the height of the weirs is such that water can freely flow between the sections. I suggest that the rectangular area of the weir (width X height of drop) should be at least 2-3x the combined area of the sump plumbing. (If the drop is too high, the water makes a more noise than really necessary and the increased water speed may dig into the DSB).

The live sand section can contain whatever you prefer. I'm going with a 3-4" DSB pre-innoculated with some bacteria from my LFS! I'm also sorely tempted to get some Mangroves floating around in there!

I'm not suggesting for a New York minute that this design is perfect - it's an idea based on other people's ideas and my own experiments, but I'd appreciate people's input.

Marc

[BubbaWPB]

Good luck Marc. Looks interesting. Let us know how well it works!