When I set up my aging barrels I put in float switches for both RO and filtered tap water. The standard float worked well for the low pressure from the RO unit but the one for the tap was unreliable and with the surface agitation from the air stone and the higher pressure it just wasn’t cutting it. So the fix was a trip to the toilet repair aisle for a old school toilet float which screws right on in place of the tiny stock one. Problem solved.