Use the sand. Just use really low demanding weedy plants they will grow. I use sago pondweed, anacharis, hornwort, java fern, anubias, duckweed, frogbit, banana plant etc. Over time (may take over a year) the sand will start accumulating nutrients. I don't do gravel vacs I only remove water when I do water changes. I don't have any issues and my tanks do not look dirty. In one of my tanks it is planted as well and I use sand and I have several rooted plants that grow fine. I use dwarf sag and Ludwigia. But my sand is mature. In another tank with sand I grow dwarf clover and dwarf hairgrass. But like I say I never gravel vac. You can use root tabs to help out meanwhile. I just wouldn't use kitty litter.