Three of my current horses and I lived on SoCal's Low Desert for five agonizing years.
A wonderful horse neighbor told me to get them on a Psyllium "five minutes ago" because we lived in sand (without any grass
For my part,this is one of those things that I believe in feeding daily. I used
EquiAid every day, on three horses, for five years. I never had one indication of sand colic or stones -- yes horses can get those too

We moved out there in 1998 and left for TN in 2003. Those horses are now 18, 25, 26+ years and still no signs of stones.
EquiAid about drove me broke but, in this case, you get what you pay for as my horses obviously came thru chaste and unscathed from that 5 yr mis-adventure. Can you tell I just loved it out there? Not----------
Equi Aid Natural Psyllium Fiber Supplements
Also:
1. Not only wet your hay and keep it off the ground in a hay feeder (I know that goes against the fact that horses need to eat "up" but you're dealing with sand.
2. Thoroughly wet the sand every time you put hay in the feeders. The horses will eat what drops to the sand. They will by nature inhale DRY sand into their nostrils while trying to get that ground hay. If the sand is really wet, it will be more difficult to inhale.
3. Lastly, something I learned from an acquaintance that moved from TN to FL: Be on the watch for sand fleas. Both her horses got them but one had such bad allergic reactions to the bites, she needed a vet
I don't know if sand fleas live in all areas of FL that don't have grass or just by the water. This lady's land was almost beach front and was polluted with sand fleas
Hope this helps
OHHHH!! You're from PA!! I moved from the PA side of the OH/PA border to SoCal. Let me also forewarn you to keep on an eye on their hooves. You're only there for the winter but still watch them. My Walkers' hooves went thru the most gross metamorphosis I have ever witnessed. I don't even know how to explain it but the farrier said it was normal coming from an environment like OH/PA has to the life in the Low Desert.
The Arab's hooves barely changed but, since his gene pool goes back to the desert anyway, I chalked it up to that. He made the living adjustment much better than my Walking Horses did.