Most canister filters go thru the media first. HOB's are the ones that the water (and sand) go thur the impeller first and will shorten it's life. I've been using sand for years and years and NEVER had a problem. Like previously mentioned, don't use the first cheapest sand you can find. You want a larger grain sand (personally I use Leslie's Pool Supply 20-grade pool filter sand) so it falls back down immediately when disturbed. Also you don't have to worry about the toxic pocket build up. These guys that gave that advice have never used a high quality heavy grain sand. I will never go back to gravel. Sand is the best.
