Hey everyone.... so Im new to this whole thing and I have a couple of questions. Is it a good idea to have a media bed to grow in, as to get the necessary bacteria to help with the nitrite and nitrogen levels? And second if I go with a raft type of system is the water constantly flowing under the rafts? Or does it drain through a bell siphon so the roots are not always in the water?
Grow beds are great, especially if you're doing a raft system as well. You can deposit your fish solids in your media bed, and then move the water on to your raft, which will keep nutrients in the fish solids in your system, rather than having to remove them all. Rafts are constant flow.
fresh water shrimp such as red cherry shrimp can also help alot by eating all the gunk off the roots.
Be sure to have an idea of what you would like to grow. Leafy greens are easily harvested from raft beds but can grow in media as well. you can easily convert a media bed into a raft bed by removing the bell siphon. If you are using a U-siphon then you will have to remove the outlet screen and put a stand pipe in. I had parsley and basil on the raft and it did OK. Not great or fantastic. It was only a month or two but maybe my expectations were too high.
As far as the roots go, Yes they are suspended in water. The raft floats on top and net pots are placed in holes if the plants are allowed to get too close to the standpipe, they could be sucked down the drain. this will reduce the flow of water and if the plant is big enough, obstruct the outlet and overflow the bed.
I just removed my lettuce last night and found several worms in the roots. I guess my dissolved oxygen DO is good. I don't have a meter but my worms seem to do well in the raft bed. fish poo will come out of the grow beds and drain into the raft bed. they will collect there. You need to have something in the raft area to break down those solids.
I am going to take a brake from lettuce this summer; Now the raft bed is a duckweed pond. To keep the duckweed in the "pond" put a larger (cap-less) pipe over the stand tub. Duckweed is suspended at the surface so it cannot go under the pipe and down the drain.