Backyard Aquaponics
A place to discuss aquaponics

Okay I think I've got the principal of the auto sipon right, a diagram would be nice. My question is on the GB's when using barrels can you leave a couple of inches below the drain point so there is always a little water in the bottom. I do this with a lot of my other potted plants so if there is a pump failure the plant can still get water. I've had 3mtr tomato plants hit the deck when a valve failed before.

leaving water in the bottom of the beds is fine.

Have to agree with OBO on this

All my GBs have ~25mm (1") left in the bottom after each drain has completed, the water inflow on the next flood cycle will mix and flush out the old water so no stagnant pockets should remain...it will also help the plants to survive in a failure as you pointed out

You don't need to adjust the siphon in order to keep water in the bottom of a grow bed, siphons naturally leave some water in the bottom of most any grow bed, the amount will be related to the size of the siphon, the rate of flow through the media and if the system is continuous flow or now. You would be hard pressed to have a siphon drain a grow bed completely dry, there is usually at least an inch of water if not a couple left in the bottoms of most grow beds.

aaawww come on ell

The diagram above is of a bell type auto siphon. Other types of siphons can be made inside or outside the bed using a loop of flexible tubing where the top of the tubing loop roughly corresponds to the high water mark. Or it can be done with pvc and elbows, again, with the top of the "hump" being what sets the high water mark. All auto siphons require a hole through the grow bed somewhere below the high water mark because the water has to be able to overtop the pipe in order to kick in the siphon.