Yes, alum is often recommended for removing glacial silt (which can wreak horrors on filters) before filtering. You can achieve the same results by letting the water sit for a few hours so the silt settles to the bottom of your container. In this case, using chlorine dioxide tablets (which also take a few hours), rather than filtering, is feasible.
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May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey