Mike, a 220 gallon sump out of 1/4" acrylic is a disaster waiting to happen. Think more like 1/2" cast with LOTS of bracing. That's 2 sheets, at least $400 worth of acrylic. OTOH, 5'x2'x2' is 150 gallons, not 220, but I'd still use 1/2" and it would still take 2 sheets. The price difference between 3/8" cyro GP and 1/2" is not enough to justify going with 3/8".

Sorry to hear about your ozone problem, losing a tank sucks.