Flat Bed Water Level After Bell Siphon Drain?

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I assume the reason for leaving some solution and not draining it all is a safety measure in case of some failure. Is this correct? If so, I guess this is system dependent. That is, if roots or wicking material cannot reach the remaining solution, no safety is created.

Do beds really need to be deeper than X inches with constant cycling for egg plant, tomatoes, zucchini, etc? That is, what is X in your experience/opinion? How much depth do you leave after Bell siphon drainage?

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I see Oliver recommends 12 inches in media beds. But, can this reasonably be reduced if you use a particularly high BSA substrate? Again, how much should be left in the bottom after the Bell siphon finishes draining?

[Oliver]

The amount you drain from your grow beds is more a function of the grow bed to fish tank volume ratio. You don't want to change the water level in your fish tank so much that is stresses the fish. If you are using a sump tank, then you do not want to vary the water level in it enough to either have it overflow or to cavitate your pump. Doing only a partial grow bed drain is fine, as after several flood and drains the water in it will be exchanged and the grow bed purged. The idea is to both purge the grow bed by bringing in new fish tank water and to aerate both the plants roots and the autotrophic bacteria during the drain part of the cycle, which also adds aeration to the water being returned to the fish tank as well as the whole system.

As to the depth of your grow beds, the deeper the better, thereby allowing time for the fish waste solids to break down without accumulating. Also, by not draining the grow beds all the way, you don't pull the solids from their bottoms.

Oliver