I had some in mine but it just blew around and made a mess so I took it out. I keep a wp-10 in my fuge to keep my cheato rolling and have lots of flow through it. Works really well.
I had sand in my last refugium tank but unfortunately after about a year it backfired and started a hair algae bloom. I ended up moving so I did not remove the sand before the tear down. I will stick to some rock to hold the macro algae and bare bottom next time.
The official triton filter would not contain sand in it. There would be two or three hand sized rocks to give the algae something to grab on to. Nothing cluttered. You want good flow in the filter as well and having the bare bottom will allow for less friction and stronger flows. The detritus would be kept in suspension better and can also be siphoned out periodically if it builds up. The tank will technically run the same with or without sand in the filter but for reasons of simplicity it is preferred to just put algae in the algae filter.