Nah no runoff. You fill the perlite bed with water and the soil wicks it up. The soil stays moist the entire time, you just keep the kiddie pool filled with water. And extra aeration is needed in the soil(extra 15-20% perlite)
Here's an example from my older grow. Just a 2"x6" frame with pond liner and filled with perlite to hold water. Pots sit on top. You just refill the perlite bed.
With that kind of setup I had issues with roots growing into the perlite.
I found a (kind of) fix for it by lining landscaping fabric over top the wick tray. I just lift the pot and the roots tear off.
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I've been watching a lot of build a soil videos and I wanna try their 3.0 and light recipe. It's the same price at my local place as Coast of Maine.
The kiddie pool should work about the same way as earth boxes, but a good bit cheaper.($12 for a 42" kiddie pool, maybe $80 in perlite) Has the benefit of using fabric pots, smaller or larger size pots, as well as a much larger water capacity.