Backyard Aquaponics
A place to discuss aquaponics

Hi all,
My single IBC AP system has been going now for almost 5 years, and 2 years ago it evolved with an addition of an small DWC (viewtopic.php?f=18&t=21254&hilit=Farmz) which did great first crop of lettuce, then miserably after, so got converted to a media bed. The RFF just wasn't able to cope with the solids, and the roots of the second crop of lettuce got covered in brown muck and suffocated.
Recently I've been given the opportunity to acquire 12 1000 litre IBC's previously used as quarantine tanks by a koi enthusiast, and a sand filter for a pool that has been decommissioned.
I'm toying with design ideas of having media beds and a 6m X 1m (approx) DWC trough. I would have a SLO from the fish tank into the growbeds, which then empty into a sump tank, where the pump would send the water to the sand filter as well as the FT. From the sand filter, the water would then go to the DWC trough and then back to the sump. By putting the sand filter between the sump and DWC, I'm hoping to eliminate the solids that will affect the DWC plants roots.
I also plan to have the Sand filter backwash into the media beds, so that any solids accumulated in the sand filter will be broken down by earthworms in the beds, and also by doing this, not be removing large volumes of water from the system.
.
Welcome any comments, questions, criticisms.

Sand filters are great at 'polishing' water and are well suited to swimming pools. This is because they have little suspended solid load and are chlorinated.

With a high SS load sand filters require significant amounts of backwash water and are prone to caking of the media preventing good backwash performance. They also require more power to overcome the back pressure of the sand bed and as such are more expensive to run.

I would try a simple vortex type chamber first or even a conventional settling chamber. Better performance could be achieved with a chamber filled with plastic media but this would require periodic cleaning. The best system I have come across for removing SS in aquaculture are microstrainers or more popularly termed rotary drum filters (RDF) Needless to say they are expensive.

By all means give your sand filter a go as a freebie, it may well give excellent water to begin with. As a long term solution though I think there are better options.

I like the idea of backflushing the sand filter into the media beds. I think you should give the sand filter a try but expect that you may have to supplement some nutrients for the DWC depending on how they are connected to the rest of the system and what you have growing.

You'll probably need to backflush fairly often which might be a concern if you're on vacation (and also a pain) - a bypass valve might be a good idea for that sort of situation.

If using the filter as a sand filter doesn't work it's sometimes possible to convert these into filters which use a floating media. Koiphen.com has some good examples of this (this is the first one I came across but there are others that might be better or simpler depending on your filter) - https://www.koiphen.com/forums/showthread.php?43524-Sand-Filter-Retrofit

Good idea of putting in a bypass valve for times I'm not able to backflush.
I was thinking backflushing once a week, but am open to suggestions.

Thanks for the link. Interesting idea.

You could set the backflush on a digital timer...

Not sure how. The mechanism to change from flow to backflush is a leaver handle that needs to be pushed down and turned.

Oh nevermind, we had one that had a switch but I guess that would not work in your case. Of course you don't really need sand level filtration to catch suspended solids, I am using a piece of PVC with an overflow valve and a couple gym socks for my mechanical filter. sounds stupid low tech but maintenance is very easy and it absolutely does work.

Nothing wrong with the KISS principle. Only reason I'm considering a sand filter is because it's being given to me free of charge.

I would give the sand filter a try , I picked one up at a sale cheap but havnt got around to hooking it up.

My plan was much the same as yours

I was going to try a bit coarser pea gravel , local gravel is a bit alkaline so would reduce my need to raise Ph all the time

I have a sand filter on our little swimming pool and send water through a solar heater on the roof , it really impacts on pump flow .

Biggest issue I think is the back pressure if you put all the water through the sand filter from your pump it will reduce pump output dramatically

You could pump to your fish tank and divert some flow through your sand filter

Another option is a separate pump for your DWC through the filter

The back flush handle system may not last long if you start doing lots of back flushes

Ive played around with little DWCs a bit over the years (easy way to keep slugs out of hearting lettuce / cabbage)

Many ways to clean up water even using a second pump lifted of the bottom of your sump a 100mm makes a big difference

Or build a radial filter just for the DWC water

Give your filter a go its all good fun.

What if I replaced the sand in the filter with bioballs (another freeby I collected)?

Thanks. Will investigate.

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If you replace the sand with bioballs the flow rate should go up significantly. Unfortunately the volume of media will still be very low and , whilst OK for nitrification, not so good for solid removal. I wouldn't recommend it.

I would try and find another tank to house your bioballs and try to gravitate the water through it using your existing pump if possible. This should keep your pumping costs low.

If you put your bioballs in mesh bags it will help when the time comes to clean it out.

(A RDF will be overkill unless you are trying to operate at commercial fish stocking levels.)

Hope it goes well.

You can make your own sieve filter (similar to drum filter) out of SS mesh pretty easily to go after the RFF.

In my original v3 plan I was going to do RFF -> Sieve -> and then possibly sock filters.

After discussing the use of sandfilter with a Koi enthusiast, I've decided to modify the filter by removing the sand and replacing with pond filter media, as it is less likely to clog quickly with solids. Still need to backwash and rinse once a day.

General design is Three 1000L IBC Fishtanks, each interconnected, but in such a way to reduce chances of fish going from one to the other. One tank for Fingerlings, one for medium and one for large sized Tilapia.
Each tank will use a SLO to carry water into two Hydroton Media Beds (1200mm X 1000mm x 300mm) (So 6 Growbeds in all.)

Each of the Growbeds will use a Bell Siphon, and will empty into one of two 480L Sump Tanks (1200mm x 1000mm x 400mm) which are connect together and have an external pump which pulls the water from the sumps and sends it to the modified sandfilter as well as some of the water will go back to the fishtanks. From the filter the water will enter one 2100L DWC Trough (approx 6m x 1.2m x 0.3m) which is raised about 485mm above ground.
The water will then flow from that DWC trough, into another 2100L trough, running parallel to the first trough, and then from there back into one of the 480L sump tanks.

Comments, criticisms welcome.

That looks like a good system. My only wonder is whether there will be enough flow through the fishtanks with only part of the output from the pump circulating the fishtank water. You will need a minimum flow-rate to be met in order for your SLOs to be effective and for the bell siphons in the grow-beds to work, and I imagine this would be easier to achieve if the water flowed from the DWC straight to the fishtanks rather than back to sump.

Ok. I haven't specced the pump yet, but looking like somewhere around 2500gph and 1/4HP.
Do you think that would be sufficient to make the SLO work?
If I have the beds as constant flood instead of ebb and flow, would that solve your concern?

Is there any formula or rough estimate as to how much water volume a media bed holds when full?

Is it 1/2 or 1/3 for example? Need to make sure the Sumps are big enough to hold the water volume if I decide to go constant flood.