Backyard Aquaponics
A place to discuss aquaponics

Hope you guys can advise. My AP system has been running for just over a year, and I'm very pleased with how it has gone. It's just a basic single IBC with pump in FT pumping into the GB, with a autosiphon, which is placed above the FT.
https://www.youtube.com/watch?v=F2rVEI0E3IM
I am helping a friend build their AP system now, and they have two IBC's and wish to have two growbeds and one fish tank.
My thought was to use about 12" of the tops of both IBC's as the growbeds. Use one of the IBC's as the FT, and cut the bottom off the other IBC and use that as the Sump. I want to use auto-siphons in the GB's.
My question is, how deep, or how much volume, should I make the sump. As it will have the pump in it running non-stop, but only have water entering it when the siphons trigger, I don't want it to pump all the water out, before the siphons drain the growbeds.
Maybe I'm just being thick, but don't want to make a mess of this job, or ruin a pump by making it run dry.

The sump needs to be big enough to hold all the water from the growbeds + a bit

Why not make the FT and the sump the same size? This should give you plenty of room in the ST to adequately fill up the beds and have extra so the pump doesn't run dry.....

If you can bury the sump partly, you can keep the sump the same size as the FT but if you can't you may be able to raise the FT higher? But this will depend on whether the beds end up too high to be viable.

But if you do want to cut the sump down use the below to work out how much volume you need..

Because were not in the 1800's anymore Ill talk in metric...

12" Gb's will hold ~250L of media (giving yourself 50mm freeboard), but you will flood the bed approx 50mm bellow the surface of the media so filling to the 200mm mark. An approx water fill capacity of 40% so each bed will hold 90L of water or 180L combined but lets say 200L to be conservative.

So your sump will need to hold 200L plus an amount to keep the pump submerged. Id go for 400L minimum. 500L would be better.

Actually doing a quick measurement in my head - you will need to bury the sump or raise the FT.

Thanks guys.
I was looking at this diagram

and I took it to suggest that the sump could be considerably shallower than the FT. Glad I asked a question.

And here's another one with the ST much shallower in depth.

Very misleading. Or am I misunderstanding something?

Hiya Farmz, they would work.
But.
You would need to run constant flood and you would need to top up the water every day in summer.
I agree with the advice for a larger sump
Go for the biggest sump you can.

Thanks Skeggley. Hadn't thought of that.
Will look at pros and cons of Constant Flood vs Flood/Drain.

I hear the sound of a probe slamming into the surface of some planet/asteroid....

Unless " means cm these days?