"i'm interested in these threads, but do you have data to support statements like flood and drain is better than cf?"

Good question. As far as data, most of the evidence is anecdotal and simple logic. It is well known that some plants won't grow well or at all in constant flow grow beds, for their roots need more oxygen than do other plants. Flood and drain supplies this needed oxygen while constant flow does not. Logically then, the bacteria living in the grow beds would do much better with more oxygen. Part of what I had edited out due to trying to keep it short was that we used to only flood and drain half of our grow beds. That was when our DO was low. Now we flood and drain all of them; and, along with the other changes, we have much better DO. It is just simple physics and common logic that the water flowing through a constant flow grow bed is not going to get as good of an even distribution of nutrients and oxygen as a flood and drain grow bed, which does a nearly complete grow bed purge.

"i'd like to see data that would support your point of view,,not trying to cause trouble or anything, but i've seen "advise" posted with nothing to back it up.. and i've seen other systems that are in conflict with your statements.."

I would be interested in the specific conflicting information and the data to support it as well.

"regarding gb depth, how did you arrive at that number?"

It is a number that has been tested by those who have been working with flood and drain aquaponics grow beds for many years. It has to do with the published surface area of the particular media with which you are working. I didn't go into the numbers here, again, for brevity. Also, as I stated earlier, I have built systems using these numbers and they work well.

One big argument is the removal of fish waste solids. Those who use deep (12" or more) grow beds generally find that they do not have a problem with over accumulation of these solids. Those with shallower grow beds tend to complain about the accumulation of fish waste solids. I hedge my bets on this by weekly adding heterotrophic bacteria, as I will talk about in a future post. After almost two years and twice in that time having to clean out the grow beds full of plants roots, I have found the solid fish waste problem not to exist. This, I believe, is due to the depth of the grow beds allowing time for the solids to break down. By digging into the grow beds while they are flooded, you do find solids in the water in the process of breaking down, but not accumulating in the bottom.

"are you selling ap products/services? (sorry, but i've been "invited" to several presentations about ap, and while they may have some good info, they have no data to backup statements!)"

Not here.

There is a lot of research available that shows the importance of DO levels needed for both plant and fish growth, and the science of nitrification clearly indicates its necessity. The flood and drain process also has been shown to increase oxygenation of the water in the grow bed, which gets returned to the fish tank. The deeper the grow beds, the more surface area there is for both the nitrification process to take place as well as oxygenation of the wetted surface area of the substrate media in the grow bed. The oxygen only goes a few molecules deep into the water surface, so the more surface area, the more oxygen is dissolved and eventually returned to the fish tank.

I need to impress the importance of high levels of DO in the system, for it is the prime ingredient that is required in every aspect of the process. Anything that one can do in the system design and operation to increase the DO will benefit the whole system. Unfortunately, this is usually mostly ignored, I believe, because of the price of DO meters.

Oliver