Hi there,
The cheapest and easiest way to make your tiles non slip is to pour is a solution of Hydrofluoric acid on to your tiles.
Hydrofluoric acid is used for acid etching tiles and has the ability to dissolve the glass that is on top of your tiles preventing them from being slippery.
Since you have a pool you are use to using Hydrochloric acid to keep your pool in balance so Hydrofluoric acid also needs be handled with the same safety precautions.