I have read that the depth of the media bed is ideal at 12". Right now I have an 18 gallon tote with red lava rock 13" deep.
The tote approx. measures 17L x 13W x 17H ( this is rough estimate, because its late, cold and dark outside, I'm warm inside)
My system has much more media in it compared to a netty pot system with the same amount of water. The rule of thumb of 12" depth seems to not apply to netty pots, yet I have seen many systems that use netty pots.
How do netty pot systems work so well without all that filtration?
I am a complete newbie to this stuff, so someone might correct me or clarify something for me, but here goes...
The other way that raft systems work without filtration is simply by having fewer fish. I first learned about aquaponics and downloaded a guide from Friendly Aquaponics. One of the things they learned about their system is that the fish were not nearly as profitable as the vegetables. So they took a "low density" approach with the fish - basically having just enough fish to provide appropriate levels of nutrient for the plants. The result was a much simpler system that didn't need extra filtration, that maximized veggie production for the money input (i.e. profit).
The benefit for the hobbyist is not profit, but just the simplicity. Although, now that I have learned more about media beds and flood & drain systems, I can see that they are very simple as well, if they are set up correctly. The biggest difference I see between the two system types now is that a media bed can support larger, taller, heavier plants. Corn (maize), for example... You can't grow corn on a raft, but you can in a media bed.
Yea, looks like you got the idea Larry.
Now back to the how can a net pot system work so well without the filtration. The answer is IT CAN'T. As Larry said, if you are doing a Low density system then you might get away without the extra filtration if the system is really balanced perfectly and as Sylvia said, the main bio-filter of the raft system is all the surfaces. Danger here is if you are overloading the system at all you will get solids building up on the roots and starving the plants for dissolved oxygen which can really hinder a system and cause a stinking mess so most raft systems have some form of additional filtration for solids at least.
Now if you are talking about the NFT tube sort of net pot system. DEFINITELY DO NOT run one of those without filtration before the NFT pipes or you will get a stinking mess. Believe me I've tested it, it may take several weeks before the stinking mess becomes apparent so don't figure that if it works for three days that it will work long term.
Each method has it's pros and cons and some mix and match can work too but one must make sure each method is getting the elements it needs in the right proportions. I'm talking about Flow, aeration, and filtration here.
Yes I did mean the raft system. thanks for all the clarification. What you all said makes lots of sense. What Larry said about the fish not being as profitable as vegetables, is true to this guy, David from Ohana Mala.