Out of curiosity, how big is your media grow bed, how big are your four rafts? No matter the size...stocking density (and to an extent, flow rate) will play a critical role in whether you may require additional filtration/solids removal. A low fish stocking density and composting worms in the grow bed would be a generic recommendation.
the growbed will be the cut off top of the ibc tank. the rafts will also be the same size (ibc top and bottom as raft). Fish density.....around 40 Tilapia 10 cm size.
Ok, so a 25% ratio of media bed to raft space would seem good. If you at all can, making your media a little bit deeper than the normal 12" should help a bit too. As far as fish stocking...I'd probably go with the lowest possible amount that I could drive my system with in order to ovoid additional filtration. I'd aim for nitrates as near to zero as possible once planted and stocked. Try it out, take readings and adjust from there as your plants and fish grow if you find that your nitrates are high, take out some fish, so as not to unduly and without reason over tax your media bed with solids etc...
The whole idea of using a grow bed to replace the filtration for a DWC system is still sort of a new concept. Well it isn't that the concept is that new but there haven't been that many large systems running that way to be able to give out firm numbers that say you need x size for y fish for Z rafts to make it all work long term without any grow bed re-washing.
It is still sort of experimental.
Long term heavy fish stocking with only a small grow bed filtering for it will probably start clogging the grow bed with solids over time so Vlad's recommendation of trying to stock the minimal amount of fish required to feed your plants is probably a good one.
I will give it a try with the media growbed, but i deciced to add a swirl filter after the mediagrowbed before it flows to my DWS, just to go for sure.
How many air bubblers would you add to a DWS bed? (size= top/bottom cut off of an IBC)?
And what i always wanted to know, is....the perlite (for insulation of walls) which you can buy at hardware store and also the rock wool which is usually used for insulate walls, could you use both for growing plants? Both are 100% natural products with no chemicals. Im just wondering, as the price is so much cheaper then in a Hydroponic store.
Perlite is an absolute PITA in aquaponics.... and rockwool can stay too wet to be used as a media...or media bed.... but can be alright for seed starting...
I agree that perlite is to be avoided in aquaponics.
I'm not sure about the rockwool for insulation being used in aquaponics. I've never actually used rockwool myself.
As to aeration for raft beds. This is really a guess on my part bot I think I've read that you want 0.5 cfm (that would be half a cubic foot per minute of air) per ibc footprint bed. So like a 6" airstone for each bed and make sure the blower or airpump can provide .5 cfm for each bed you have at about 1.5 psi. And you probably also need about 1 cfm at 2 psi for each 400 gallons of fish tank.
And now I think to check your profile and realize you are not in my part of the world and so all my numbers being imperial are going to give you a real headach in translation to metric so maybe someone who knows the aeration recommendations for raft aquaponics and thinks in metric might chime in and give better numbers than I just regurgitated.
haha....thanks so much TC, dont worry about the numbers, i have a converting program :D Well, surely i would not use perlite as growing media for the media bed (substrate will be hydroton). I would use perlite as substrate for the small cups in my floating raft. Could you please explain me why perlite is a PITA in AP, John? I tried it once in my a NFT system, and i thought it works fine. How was your experience with perlite? Is perlite for insulation the same as the perlite sold in hydroponic store? Thank you for your help, always very thankful for sharing your experience;
Since perlite tends to float and break up with any rough handling, it is likely to escape the net pots and wind up floating around the system. It is hard to contain and remove once that happens and it can get wedged into mesh protecting the drains and perhaps even make it to the pump which wouldn't be good for the pump.
When handling it you have to have a spray of water keeping it moist since any dust from it that you might breathe is very bad for your lungs and I don't imagine the dust from it is good for the fish gills either so most people will warn you strongly against using it in your aquaponics system.
I don't know if there is a difference between the stuff sold for insulation and the stuff in the hydro store but no matter where you get it, I don't recommend it.
And depending on the size of the net pots you are looking at using, If you start the plants in starter media that is big enough to hold stable in your net pots, you might not need any additional media in the net pot beyond whatever you start the seeds in.
I have been using media beds for filtration for DWS for more than a year now. I recommend that a minimum of 25% of the total grow space be media but more is better. If your fish tank is at the lowest point then all the solids are run through the pump and most of it is liquefied. I would use several media beds and an indexing valve to time the flow to different beds to give the worms more dry time so they can keep up with solids that are caught. I use a swirl between the media and rafts to eliminate any left over bits.
For aeration I use an O2 meter to determine my needs and have balanced my troughs accordingly.
Thank you Chris, TC.....what do you use as media in your floating rafts? what is your choice of starter media?
I use small black cinder. It has great wicking properties. I seed net pots directly in rafts and float then immediately to hydrate the seeds. The cinder wicks water up but the voids in it keeps seeds from being too wet and rotting