Below you will find a couple of ways to use old aquarium gravels.
First, make an umbrella stand. All you need is one large vase or other tall container. Fill a quarter to half of the vase with aquarium gravels. Umbrellas can then be pushed into the gravels for storage. The weight of the gravels will also prevent the vase from toppling over.
Second, make a candle holder. Fill the bottom of the vase with gravels and place a candle inside.
Maybe I should have called this post “What to do with an odd shaped vase”….!