I agree rice hulls are a really good amendment. I find they are the best to break up either compacted or gummy, clay like soil and on a volume per volume basis are highly effective, even more so than coco. Where coco shines is it's moisture retention. But where rice hulls really shine is when they decompose their NPK is 1.9-0.48-0.81, C:N is 14:1, ph is 7.0, it's like the gift that keeps on giving, and especially good flower ratio and since it's there in volume it's overall amount for npk is actually quite a large reserve of slow release nutrients. All really good numbers along with micronutrients, the same can't be said for coco. When coco fibres break down they end up consuming more ca,mg which if your in tune with shouldn't matter but you have to babysit the soil with coco. Rice hulls also feed the food chain with a mycelium mat but coco when mixed with soil 40:60 ratio has given me earthworms.
Research article on rice hulls:
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Its got me thinking from my two soil recipes, one a coco based modified subcool soil and the other a rice hull soil in the SIPS that a 10-15% coco, 10-15% rice hull, 10-15% pumice would be an ideal soil for a 12" high pot, sip or no sip. My subcool soil in a plastic 15" high pot is moist right to the top and plants are waterlogged a little too much. My fabric 10 gal (12" high) rice hull soil is dry for first 3-4 inches, my modified subcool soil in fabric 10 gal pots (again 12" high) is moist to the top with surface roots under the plastic cap. Possibly too wet below but plants seem to be doing good in it.
The roots don't circle the pot in my rice soil and in a plastic pot it acts more like a fabric pot. Coco does circle the pot moreso but nowwhere near as bad as a heavier soil. Pumice, perlite don't even come close to providing this as rice hulls. I do add pumice just to keep a base level of aeration once the hulls decompose and it works well in a sip wick. A 60% dry peat to 40% pumice sems to work well as a wick.
Find rice hulls at a brewers store, not all carry it ime, about a third of the places I contacted do and two places were willing to sell a 50 lb bag to me, one of which I picked up for $50.