Backyard Aquaponics
A place to discuss aquaponics

Hi y'all,

I'm new to aquaponics, but not new to recirculating fish systems (under gravel filters), and not new to soil based vegie growing. I'm in the process of building a largish system 4,700L FT + 500L fingerling tank with 10 x 500L GB's. It's a media based system, so ebb and flow with 'blue metal' with expanded clay on top. The grow beds are deep so the bottom 600mm is the 14mm blue metal drainage gravel and the top 300mm the ECP. Plan to house the fish tanks and build poly tunnels over the grow beds to extend the seasons. Silver Perch and Eel Tailed Catfish are the best choices for my location and needs, but if I run another FT (probably will) I will give trout a go in winter. Location = southern NSW between Yass and Canberra.

The plan is to raise food for family and then move into small scale commercial production, but not raft based as I plan to sell any surplus at the local farmers markets and want to offer variety. Rafts seem best suited to monoculture. I know all advise to commercial growers is to go for rafts because they are easier to manage and offer more $$ per m2 etcetera, but this is not about money alone.

Anyway so far all is going to plan and have acquired most of the bits and pieces, just waiting on the main FT which is a Rapidplas 4,700L squat rainwater tank (I'll cut the top off). Now to the only question I haven't been able to glean from the 4 books two dvd's I purchased and many hours of lurking. Do I filter the FT water before it goes to the grow beds or not??? It's easy enough to filter out the solids to approx. 50 micron, but should I? I like the idea of using all the waste within the system.

Consensus is you definitely filter the water if using rafts or NFT, but with grow beds the opinions get murky . Some say filter the water or the beds will clog, go anaerobic and toxic within a short space of time. Others say let all the nutrients flow into the system and have the bacteria and plants take care of it. My experience with under gravel filtering is that this doesn't happen at low fish stocking densities, but it does at higher densities. I'm sure stocking density is the key, but surely every time a plant is harvested some to the roots and root hairs will remain behind, break down and eventually clog the system? Or is everything broken down by the bacteria and recycled?

Any and all advice on this greatly appreciated. Oh and while I'm at it, red/compost worms in the grow beds? Do they help a non filtered system? Do they help keep it clean(er) and or aerated?

Cheers, MC

Flood and drain grow beds really do not require filtering. You can add worms to the growbeds to process the solids. The solids are needed to provide nutrients as they mineralize. The water will stay clean and clear as long as you dont have a run away algae problem.

Now, having said that, my personal opinion is that partial(but not complete) removal of solids is a good thing. It just makes life simpler for me.

Welcome mcfarm, BTW

I do both as well. GB's for most of the solids and a 200ltr swirl filter to catch some also. Later I will be connecting a 1000ltr swirl filter to catch even more of the solids so they can be incorporated into compost and worms farms directy.

One of the main benefits of flood & drain media based growbeds... is that they don't require "pre-filtering" McFarm...

It seems to have become somewhat "popular" lately to filter some solids, for various reasons...

But IMO... with a properly set up system... it's just not necessary, and much of the mineralisation that provides micro-trace elements takes place in the growbeds...

Worms definitely assist this process...

Swirl filtering, and other external filtration is definitely required for NFT and DWC raft systems...

And as suggested by DanDi... does allow a greater margin for error, in terms of water quality management.... or for increased stocking densities....

The downside is perhaps the increased plant trace element deficiencies... and need for increased supplementation...

In some ways, in comes down to just where you aim you focus.... toward fish production or vegetable production....

And just how "closed loop" you want your system to be....

I think most of the discussion about pre-filtering is aimed at water going directly to Rafts DWC beds or NFT troughs or towers etc. Or even situations where stocking might have surpassed immediate growbed capacity.

Actually, a nice media filled flood and drain grow bed makes a mighty good pre-filter for many of the other methods. Definitely adding some composting worms to each grow bed is a good idea that can help keep any build up of solids from becoming an issue.

Then again, I think some people like to do a little pre-filtering because they actually want to use the solids somewhere else than their grow beds. In which case it isn't about "protecting the growbeds" but about feeding the worm bin or giving some dirt garden plants an extra treat.

showing my naiviety here - wouldn't worms drown???

Worms live quite happily in water... as long as it's oxygenated.... and the flood & drain action of the growbeds does just that....

They live, they feed and they muliply.... it's all good...

Na these worms are living 1 metre under water

Thanks all, much appreciated.

Would much rather not filter, but don't want to have to clean out grow beds every few months - every few years would be OK I suppose. I'd like the system to be as closed a loop as possible; fish food in, plants and fish out, and the system to deal with the waste via recycling/conversion. OK so I want my cake and to eat it too, but it appears possible if the system is not pushed too hard. It's how I run my farm anyway - not pushed hard, plenty of buffer/give/forgiving/spare capacity.

So I will 'suck it and see' unfiltered. Worst case I have to back wash the beds and add a filter at some stage.

Thanks for the warm welcome too DanDMan.

Most people have found that unless grossly overfeeding... which reveals itself in other nasty ways... there is no need to "clean" the growbeds for several seasons...

Usually, any that do, do so when the beds are "barren"... just before a replant...

Again... it's all about a balance.... and that's the holistic beauty of aquaponics... it mimics a balanced natural system...

1 Metre under???? did you empty that tank Milne?
If not, how on earth did you keep the trout and perch from eating them all!?!?!

hi Kuda they are in the filtered water sump just before it goes back to the ft

If you wanted to put in a DWC gb would the exchance of water have to be very high. Cos having the water first go through a normal gb and then into say a 200ltr drum with an overflow and a filtered feed to the DWC tank. Then the water would slowly turn over in the DWC tank but most of the solids would be taken out before hand. You would still have to clean the filter every few days or once a week. I find the water that goes out of the gb's through a filter mat does not need a lot of cleaning. The filter on the inlet clogs more often. And this is mainly aglae.