Backyard Aquaponics
A place to discuss aquaponics

For my situation since the tires or pallets would be only the support under the grow beds, there would not be the chemical issue but the other half does not like the use of tires in landscaping so I've never been allowed to use them.

mrgrackletx,
The good 45 mil EDPM rubber liner I've found for as little as 40 cents a square foot. Plus shipping comes to less than 60 cents a square foot. I've tended to go kinda long and narrow for my pond/tank and grow beds for two reasons, liner tends to be a little cheaper in long narrow roll type shapes and it is easier to reach the middle of something less than 3' wide.
You are right that in estimating the size of liner you need you should figure the length + 2x depth plus 3' spare and width + 2x depth plus 3' spare. This is how they usually tell people to do it when they are digging ornamental ponds.
I'm being stingy and going to attempt the grow beds with far less than the advisable amount spare. Hopefully my luck is good and the liner really is as big as it is supposed to be. I'm figuring that with only 1' of depth within a wood box, arranging the liner can be carefully done so as not to need the extra 3'.

I think you`ll be ok especially on a warm day as it stretches a fair bit
I guess their extra 3ft allowance is geared to a paving slab perimeter rather than a timber rail fixing.

My guess about the 3' extra is more that most people are putting liner in ground and the average home owner putting in their first ornamental pond isn't going to have planned so well and if the liner is only just barely big enough, there is no way to use rocks around the edge to hold the liner up from falling into the pond. Also, it is tricky to dig exactly the perfect hole in most ground so some play is usually needed.

Maybe Suspending gravity is not what you want to do, since water will always seek an equal level in two tanks that are connected, but rather use gravity to fill the growbeds, and a pump to drain them....

Hay Clovis,
I suppose in my mind that looks like a CLFT PIS set up. Constant Level in Fish Tank Pump In Sump. To pump out of multiple grow beds with only one pump, I would figure a sump is needed and that is where one would put a pump on a timer or float switch.

Anyway, the idea is good and I like it but the drawback is how to have a tank in ground that is not always full of something. What happens when it rains heavily and the ground is full of water? The tank will eject itself from the ground.

I suppose the other way to look at it is that the grow beds are simply connected to the pump with plumbing. Hum, an idea to think about.

My current big system isn't really set up to operate that way but I may have to think more on it once we build the big house and move.

I prefer to have the pump run all the time as that provides continuous aerating to the pond through the bypass. The auto siphons allow the beds to drain onces they fill and everything functions with only the one pump. It just requires that the grow beds be far enough above the tank to allow the auto siphons to work and drain into the tank.