I slice the top off my barrels as the lid will neatly fit when you turn it over.
Don't keep your barrel air/water tight as the K1 will rise as it gets clogged. Even churning media needs the occasional super boil to unclog.
I tek screw 4 lengths of 15mm PVC pipe vertically at 3, 6, 9 & 12 O'clock around the barrels to slide airline down from above. The pipe is to hold airline in position, equidistant apart and at preferred depth(s). No airstones.
If you have your barrels above water line, drill a small drainage line (4mm) that constantly bleeds back to your tank. If (when) your power fails, the barrel will slowly drain water out so the K1 doesn't suffocate. It will still stay sufficiently wet for 7 - 10 days without power. Easy reliable safeguard without any moving parts to fail.
If you have valuable fish, use 2 separate barrel systems for redundancy. I use 2 air pumps per barrel as well. And a secondary barrel of static K1 for mechanical filtration.