This year is my first experience with Shimpakus so Im no expert yet lol.
A little Yellowing is a normal phase in Shimpakus. as long as theres not a whole lot of yellowing its nothing to be feared just watched.
The Setting for my area for Shims is morning sun to afternoon shade.
Water each day (depending on soil) twice if temps get over 100.
Free draining soil is a must as they dont like to be soggy. As Tachigi suggested Akadama/Kanuma is golden for shimpakus.
As for Oil-dry, We can all go on a debate romp about Oil Dry this oil dry that. There are MANY many variations of the product that are fired at different cone temps. The one that was highly suggested to me, and I suggest to you is the product Oil-Dri. That is if your looking to start making your own soils. Its Available at Sams Club in the automotive section for $3 and some cents for a 40lb bag. It is fired at a consistent level and even mentions it could be used for gardening. Seeing as this is my first season on making my own soil (have 3 kids now so no soil fundage anymore) I have a few testers going with broadleaf cuttings. if by next year theres sludge or anything unworthy, I will note it and let yall know.