Is doing this okay?

[greenknight]

Using pure grit to root in just means it won't hold as much water, so if you overdo the watering it's less likely to be a problem - more margin for error. Should root just as well in your mix. The drying up of the leaves occurs because the plant needs to get moisture from somewhere, but it has no roots, so it takes it from the oldest leaves. It's also reducing it's moisture requirements by casting off some leaves.