Heh.. I just converted my 80g and my 60g from gravel to sand. The 80g I filled using cheap sand from home hardware, as there was nothing else available in town and I didn't realize the better stuff wouldn't be out for a couple more weeks.
After putting some sand in a 5g bucket and rinsing throughly( about an hour per bucket) reapeating until all 120lbs were cleaned I put it in my tank. Filled the tank up and left it thinking it would clear overnight. We put a couple small HOB filters in with some filter wool to help just in case. The next morning it hadn't changed a bit so we did a 50% water change(we used pure cold tap water for convenience as we already had a suspicion at this point it would take a couple days) and left it until the next day. Same thing for the next week, changing the filter wool about 6 times daily. On day 8( I think it was, maybe 9) it was finally clear woohoo. So we filled it up with proper temperature water and it turned as dirty as ever. Warmer water absorbs more particles
I cant even remember how much water we changed that day or the next... spent several hours each day filling the tank to half then emptying it again disturbing the sand as much as possible to get all the fine particles we could. I'm sure we did at least 500g a day for those last 2 days. At last it was clear(Aside from the gas bubbles, which left the tank almost a milky white) and the sand could be disturbed and it would resettle in seconds, even in the hottest tap water possible.
For the 60g, there was more selection for sand at this point and we picked up Sakrete fine sterilized playsand.We only had to rinse this in the buckets for 10-15 minutes before it appeared clear and then once in the tank we did a 50% change the day after and I think it was 250% the day after that and it was all cleared up.
Many recommend pool filter sand but I have eels now in the 80 and loaches in the 55 so I was concerned about how sharp the pool filter sand might be. It apparently is much easier to clean then playsand. Also actual aquarium sand is good as well but it does cost a fair bit more.