So as my reservoir is too small, we have decided to get a Rubbermaid Stock Tank, a 100 gallon.
We were thinking about trying raft aquaponics (er, not sure what it is actually called) along with our flood and drain media beds.
So that would lead me to believe that there is more fish needed, and I am unsure how many. How much should we up the stocking density? Or what is a good balance to have between fish and plants? Will the plants in fact clean the water enough to justify more fish, or would the water not be suitable?
Or even if this is a good idea to try. I do not know if all the plants would be getting enough nutrients, and I know near next to nothing about raft hydroponics, as this is a freshly formed idea, I am still unsure of many details.
Stick with the stocking density for the amount of media bed you have to start. Get the system cycled up and balanced and then figure it out from there.
Once the system is cycled up you can figure out how your nutrient levels are doing. If you have measurable nutrient levels, you might be able to add plants to a raft bed. If your nitrate levels are reading 0 and your plants are showing signs of nitrogen deficiency while your ammonia and nitrite levels are 0, then you might add fish or feed your fish more (but only if they will eat it.)
Don't worry about dilution, this is really only an issue if you are not filtering enough water to keep it from getting scummy. Raft systems generally have a huge amount of water.
Make sure the water gets filtered before going to a raft bed and raft beds generally need additional aeration.
You can only up your stocking density in a fish tank to the extent that your circulation, filtration and aeration will support the fish. Very heavily stocked fish tanks are going to need careful monitoring since a short power out can quickly mean depleted oxygen and dead fish especially if the water is warm.
But I don't believe excessive stocking is necessary when you are using flood and drain gravel beds as the basis of the system. My systems have usually had enough nutrients left over to add additional planting methods like NFT and now I'm testing out a raft bed as well, all getting water filtered by the media beds. Since media based aquaponics leaves the solids in the system, there is an extra nutrient supply as the solids break down and fewer fish are needed to support the same amount of plants.