Either get a sponge filter sleeve to go over the strainer or use a whiffle ball and an old section of nylon stocking. Drill a hole in the whiffle ball the same diameter as the strainer, pull the stocking over the ball, slide the ball onto the strainer, and zip-tie the loose nylon edges to the lift tube. The fry won't get sucked in and the filter won't strain from the nylon addition since the whiffle ball has more opening surface area than the original strainer.