Sand isn’t the best choice unless it’s in water proof containers. My weights are bleach jugs with a mix of sand & concrete. The lids are capped with duct tape before putting the cap on (cuz bleach jugs are vented). I hang mine from a rope attached to a hole in the back of my steps since mine don’t have a bottom to set weights on.
In the ballast that sits in one of the steps I have sealed country time containers filled with sand. The pool people just filled it with sand initially even though I tried to object. It became algae city very quickly. I guess they didn’t care because it’s not their pool
they just wanted to be finished installing. They also said that tiny cylinder of sand would hold them down- nope
Depending upon the configuration many people have done filled & capped pvc pipes as weights.