Backyard Aquaponics
A place to discuss aquaponics

Ok, back to positive comments

here is a link to an easy-to-build DIY fluidized bed filter
http://www.cichlid-forum.com/articles/diy_fbf.php

I think this combines the advantages of sand as a filter medium, eliminating anaerobic issues which I am not convinced are a positive addition in the closed loop since, from my limited knowledge, the anaerobic process reverts nitrates to toxic nitrites.

Frank

Do I get to wear those funky spikes on my shoes and walk on my grow bed?

I'm actually thinking that some perferated corrugated drainage pipe down in the sand bed might be a simple option. Like a line of it from where the pump inlet is to near the siphon so there is a relatively direct way for liquid to flow through and let the solids down to the rest of the system and the sand on either side can wick up moisture and perhaps drain a little easier.

Gotta run for now, keep thinking!

TC, you are thinking exactly along the same lines as what I've been thinking. You could make a "plenum" at the bottom of the bed by placing drainage pipe side-by-side at the bottom of the bed, to make sure that the water all drains out, as much as possible anyway.

Another thing to try would be to flood the sand beds less often than you would for gravel beds, to make sure they dry out. This might be bad though because the water wouldn't be forcing gasses or stale water out.

If you want to use sand but are not married to the sand you have already then maybe a coarser sand would work better, like almost gravel.

Dont forget the find the geyser pump thread.

Geyser Pump experiments: http://www.backyardaquaponics.com/forum ... 45&start=0

full anerobic conditions will revert nitrate to nitrite, anoxic (very low DO) seems to go to a N2 production. differnt bacteria and granted a hard conition to maintain.

i like the submerged pipe idea. maybe a loop or two of aggie pipe with one end connected to the drain point and the other left open above the top of the bed level. water would trickle into the aggie pipe and be open to fresh air.

i also agree that the choice of sand grade is going to be an important choice.

RE: fluidised bed filters, to my knowledge they provide incredible surface area to volume ratio for beneficial bacteria, and also grind down solid wastes, but dont actually entrap any solids, so the ultra fine solids may still pose a problem for the NFT roots

TC, just looking at the photos of the hole (jealous by the way of easy digging ) how coarse or fine is your sand? and is it "dirty"? By that I mean, when you drop a handful in a bucket of water, does it take ages for all the silt to settle down in the water?

If the sand is very mixed sizes, with lots of fines in it, it will take a long time for your system water to clear. You might want to grade the sand through some sieves to get the coarser stuff for the grow beds.

I was planning to attempt some grading of the sand before putting it into any system (even if that meant putting it into a bed or trough and flushing water through-not into the system- to wash out some of the fines.) The sand has some fines in it but if I choose from the yellow/orange layer it is a bit more medium. I need to do some more tinkering with it though.

It is pretty easy digging, that is a good thing. Drawback, in areas that are very sandy like this, rocks and gravel are hard to come by.

Luckily, whatever I do, there are no fish yet to kill.

I'll send you some rocks

Today's test results
ph 7.8 - 7.9
Ammonia 2 ppm
Nitrite 2-5 ppm
Nitrate 5 ppm (I do have plants in the system so they are probably responsible for this going down)
Was a bit warmer today and supposed to be so tomorrow so hopefully the bacteria will get a move on.

nice middle of the cycling road

You can buy sand blasting sand/silica of various sizes. Its uniformly sized and here is $6 per 50 pound bag. I found that using this stuff as a hydroponic potting medium was not a great idea because it did not not stick together so well and flowed out through the holes in my cups. Should work great for a sand filter.

Ouch[schild=17 fontcolor=000000 shadowcolor=C0C0C0 shieldshadow=1]Ouch[/schild]

Anyway, got the bell siphon to work.

Sand Testing

If you thought washing gravel was silly, I have now washed sand![schild=8 fontcolor=000000 shadowcolor=C0C0C0 shieldshadow=1]Wash this[/schild]