I am looking for ideas that would work as a perlite substitute. So far all I can think of is cheap cat litter that is well rinsed off. The other thing is aquarium rocks. Will either of these work and if not what would be a good substitute?
you should be able to find perlite at any garden shop. none of your subs will work cause they don't hold water and aren't light and airy like perlite is.
I shy away from vermiculite, it can whack your pH. You should be able to get perlite at Home Depot, Lowe's, and garden stores. I got some at HD just this past week. Walmart/Target/K-mart/etc carry it seasonally.
cat litter is about the OPPOSITE of pearlite! pearlite is like a rock sponge. it's very porous so that it drains easily to keep the soil well aerated. kitty litter on the other hand is really just clay which makes for TERRIBLE soil. kitty litter would retain moisture and if it became moist enough to dissolve, it would choke your soil. i've never had any problems with vermiculite in previous soil batches myself. i've used generous amounts of both that and pearlite often, but that would be the opposite of pearlite too because vermiculite is used to retain water. you might want to try and look for soils made from composted bark fines. those drain extremely well and are light and fluffy. in fact they drain & aerate so well that they dry up quickly if not watered.