craftgrrl | wedding centerpieces with sand (Reply)

Hey crafters! I'm the matron of honor in my best friend's wedding and I'm trying to help her and her fiancee with their centerpieces. They are having a beach wedding and they got fish bowls, sand, seashells, and floating candles for their centerpieces. They want to put a layer of sand and a few small shells in the bottom of each bowl, fill it with water, and put the candle on top. Is there anything we can mix with the sand to make it solid at the bottom so it doesn't make the water murky? My initial thought was mixing the sand with water and Elmer's glue, but Elmer's is water soluble so the water in the bowl would probably end up with some glue in it by the end of the night.

I also thought of maybe mixing the sand with water and Elmer's, putting it in the bowls, then putting a layer of something over the sand once it dries. Maybe Modge Podge or something? Would the water penetrate through a layer of Modge Podge? I wish I could be doing mockups of this but my friend and her fiancee are quite a ways away from me right now and they have all the supplies. I'm just a crafty consultant. ;) Any ideas on how we could make this work so the sand isn't making things all murky when the bowls get filled with water at the venue? Thanks so much for reading!

ETA: I've suggested rinsing the sand first. [I use sand as a substrate for my saltwater tank and I had to rinse it at least 8 times before the water stopped being gross.] I think they're more concerned about the sand kicking up when the water is added, so we're looking for a way to prevent that by either adding a protective layer over the sand or mixing the sand with something to make it a solid.