What is sts look like? Is it the one made of clay? Does it break down? Are you using it alone and as a cap for something? Did you get it locally?
ill snap a photo for ya but there are plenty on tpt. Its made of calcium montmorillonite clay, high cec which is great for precharging. there are people that have used this for years without breakdown which is why i went with this. $10/40lbs shipped online. anywhere other than NY, you can likely go to a supply shop and pick it up a 40lbs bag for $4... mine seemed to be sold through Grainger's when it arrived.
Using Oil-Dri for cheap substrate?
Oil Dry - Safe-T-Sorb