Are you gonna go with stems, swords, or any crypts? Or just mosses, anubais, and java fern? Also do you want an inert substrat were it doesn't lower pH or do you?
If no to noninert go with Ecocomplete or Flourite. If you want your substrate to lower your pH, there is all those stratums like Fluvals (Fluvals Stratum has little nutrients, so use root tabs!) or you can use Azoo Plant Grower Bed (Should be $31 shipped) this does have nutrients.
I wouldn't, crushed coral is going to make your hardness go through the roof. The only time you should add crushed coral or shells is to increase or stablize kh or gh, only a small amount is necessary. The only fish I would use crushed coral for is cichlids. Though it depends, is there salt in the corals? Will they provide salt to the water? I would do some tests to see.
Best bet is to sell it on Craigslist and buy a bag of play sand at home depot or Lowe's for low $5 for a 50lb bag. It won't raise your th or kh unless by a very very small amount. And it looks good.
Hey, I have a question and was referred to you. I have a 40lb bag of crushed coral. It was originally bought for a saltwater tank. Can I use that as substrate for plants provided I add fertilizer? The bag says it will maintain a steady ph. My ph is 7.0 without it. Thanks!