Hi, and welcome to the forum!
Can you specify what test kit you're using, and give us a set of test results (numbers, not "spot on" or "great") to look at? If you're having algae problems, then your chlorine levels are not being kept high enough (or perhaps you're not holding shock level long enough to kill it all off).
It's entirely possible that yuor pump is just oversized for your filter, and is driving the debris right through the sand. Does the problem change at all when the filter is backwashed? Is your pump pressure rising as the filter is running, and does it come back down after backwashing and rinsing?
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