Backyard Aquaponics
A place to discuss aquaponics

If you did, how would you establish the water level without the "pipe in pipe" method? I was hoping to use the existing IBC drains, but can't figure any way to prevent them from emptying if the pump stops working.

Just put the SLO on the outside of the tank.

90 degree bend on the outside of the drain, pipe across the bottom to the side of the tank (don't need this piece if the drain is in the side)
90 degree bend and pipe up the outside of the tank to the water level
tee piece vertically at the level you want the water
drain off the water from the side of the tee - leave the top open to prevent a syphon

You can get an ibc to 50mm adaptor which you could then plumb in a 90, a stand pipe, a tee to set your height and then plumb from there. I'd be worried about fry or fingerlings getting stuck in there without a filter or screen.,

I have 6 of these, so I'm not sure if I have enough space to do external standpipes. But possibly an SLO and capping off the bottom 50mm coming from IBC? Wanted to use a 15/85 split bottom to sidewall drain, so I will probably need to just cap those off and do the thing the way I first had planned.