Changing from gravel to Sand

Pool filter sand is better than play sand. Its going to be quiet a challenge putting the sand in an already established tank. I reccomend taking the fish out, dropping the water lever 3/4, removing the gravel, and putting the sand in. Refill the tank and let teh sand settle before turning your filter back on. Then put the fish in. This will be the easiest way to do it , and IMO, the les stressful way on the fish. Expect a mini cycle tho...

i agree with blueiz

if you can drop the water down to about an inch, it makes a huge difference. and removing the fish keeps them from freaking out.
also, consider taking a couple handfuls of your old gravel and putting them in a nylon stocking/sock and droping it in your tank for a couple weeks.. that'll help the new sand cycle more quickly.. it doesn't look very pretty.. but it does the job.. if you can fit it in your filter that would make it less noticeable.

I have play sand in one of my tanks but I hate it because the granules are very fine, they kick up easy and make the water cloudy, and they can get in your filters impeller and damage it.

You can get a coarser grain "All-purpose" silica sand at Home Depot/Lowes for about the same cost as play sand.. also be aware that if you dont get bagged aquarium sand, you are going to need to wash it quite well.

i usually use 40 to 60lbs of sand.. the finer the sand the more you'll need

Theres a substrate calculator on here is what i go by....:http://www.plantedtank.net/substratecalculatorcalculate.php?width=48&length=12&depth=3&substrate=60

I did this not too long ago. I had a fully established tank for over a month and wanted to change to sand. I bought some pool filter sand, cleaned it out, put the fish in a bucket and started draining. When the water level was around 2" above the gravel I started pulling it out with a strainer. Once it was mostly out, I just drained the rest of the water, brought it outside and washed it out completely. Then I added about 3 or 4 inches of water, and then 50 pounds of sand for my 55g. I added the fish once filled and then turned the filter on about 10 min or so after being completely filled, and the water was clear very quickly. I never had a mini cycle or anything. I have a penguin 350, and live plants so they were able to handle everything. The whole process took about an 45min-hour but it was well worth it I think. Also if you are worried about a mini cycle, just put some of the gravel in pantyhose or something and let it sit on the bottom for a few days. That will help the bacteria resettle.