When you replaced the sand, did you use pool filter sand or another type? While you had the sand out of the filter, did you inspect the laterals, and were you very careful when you refilled the filter not to damage or move them? When you started up the pump for the first time after the sand change, did you start it up in backwash, and then rinse modes before changing back to "filter"? Do you actually see it blowing into the pool--if so, is it constant, or just during the first few seconds afer the pump starts up? What size filter, and what HP pump do you have? Did this ever happen before the sand change? What was the reason for the sand change?

Just a few ideas....

Welcome to the forum!!