That's weird because all accounts that I've heard about the vortechs suggest that the flow out the powerhead is so gentle that sand blasting wasn't an issue. In fact, someone had a shallow tank of 12 inches while running a vortech and said that sand blasting wasn't a concern for them. It looks to me like your vortech is pretty high up and it still blasts the sand? So maybe just try a heavier grain of sand?
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