Backyard Aquaponics
A place to discuss aquaponics

Oh OffGASSING yes of course! :-)

perhaps I could change the design somewhat.

Do you think clogging could be reduced by having a low flow high pressure water stream and force it through the media?

This would allow offgassed nitrogen to pass out the top, and if it starts to get blocked, you can see from the outflow, so open the inflow a touch more, or regularly 'flush' it with high flow.

Think there might be problems with O2. Have an article on deep sand beds somewere if I find it I will post the link.

Sounds like a recipe for a sand-cannon, KP.

You want to ensure that flow is slow to encourage anoxia. With high pressure, I don't know how you keep things slow unless you have back pressure.

Sand cannon rofl!!!!!
very low flow, so no cannon. As you said low flow is required... sand cannon -smirk-
I now can't stop picturing a big blast of sand erupting from my device hehehehehehe

I was thinking back pressure yes. simmilar to pressurised cannister filters. it helps make sure the water gets everywhere, but slowly :-)

This page isn't exactly what I was looking for but at the top of the page there are many links about it . Mainly marine stuff but interesting.

http://www.wetwebmedia.com/deepsandbeds.htm

Good link Sleepe - just confirms the theory.

Yes, a good read Sleepe

They only do it for the nitrates though, the chelated iron and carbon was very interesting.

Random thought that it may be possible to put in a low flow over a deep sand bed and grow mussels or clams on top, extra produce and cleaner water?

Sounds good, Sleepe. Go for it.

Yep, after reading about deep sand beds I had been thinking about just adding a low flow storage tub with sand on the bottom, with a grow light to grow duckweed to get dual use out of it. Never tried it though.

Just a suggestion for the Chelated Iron crowd.
If not using cast iron swath (which I can get for free for APers in Vic if you're interested) Why not use steel tube as your RSG instead of PVC pipe with steel in it... then when it's done it's job, the steel will be gone. Course you'd have to add a lot of carbon over time to eat through even 1mm wall thickness, but just trying to simplify things.
Offcuts of hollow section steel are not hard to come by - often for free.

Just a thought - for low-flow, why not put an RSG filter in the sump or tank where the water level fluctuates? Have the top just shorter than the high-water mark, and the sand start just below the low-water mark. That way, you would have a few inches (cm) of water pushed through the column each pump cycle, but if the RSG is away from the inlet and outlet, it would be nearly stagnant, thus giving you the low flow.

I tried that with a planter full of sand but my sump didn't go up and down much.

If I were to try another RSG filter I would take a big pipe and cap both ends, with an inlet and outlet at each end to make a flow through filter. Set the pipe on its side full of sand, but with an inch or two of open area at the top to let the water flow. That way it may limit how stagnant the sand gets - maybe it would perform better because the pipe could be 4 feet long instead of limited by a grow bed's depth.

Would you put one RSG filter into a system or one in each bed? Also, if I wanted to make sure of iron availability (for citrus trees), would I put one of iron in each citrus tub or again, just one in the system?

HD, I don't think we really have enough data for metrics on an RSG filter. We only have limited data that maybe supports the idea that they work. I wish I could tell you exactly how much RSG you need, but I can't. Take some data points for us, OK?