I got some Red Flint sand, and I love it. I didn't rinse it at all, just poured 2 bags in. Tank was completely cloudy for several days, and I did many water changes to clear it up, even with my FX5 running the whole time. I have 2 more bags to put in, but I will definitely rinse it all before putting in the tank. I am going to partially fill a 5 gallon bucket with sand, pour water in there and shake until there is no residue left, then pour in tank. Yeah, it's gonna suck, which is why I haven't done it yet. lol For my 125 I have 2 50 pound bags in there right now, and it's a little thin for my liking, so I'll probably put another bag in and see how it looks. My fish can wash the sand away to the bottom pretty easily, so I like a little more in there, plus you can sink down driftwood and plants more.