DO NOT WASH IT!!!!!! You need all the "stuff" that's in it. I say stuff because their is a ton of good stuff in it like nutrients, small live critters and some not so small. I found a cool black nudibranch about 1in in length. I didn't know what it was until a fellow member ID it for me.
I have about a 1/2in-3/4in base in my 20 long.
I ended up going with Miracle Mud, just because it was on sale at the time. I've heard good things about both brands. Been useing MM for almost 2 years and like it.
They sell a "recharge" jar of it as well. It is pretty much the same thing but highly concentrated. You could probably get away with buying a small jar of that stuff and mixing it in with some live sand, but I haven't heard of anybody doing it this way. Would be cheaper though.
When setting up my tank I was also concerned with it causing a cycle. The guy at the LFS said it shouldn't, so I went with it. After a day or so I started getting readings of phosphates (sp?) and nitrates when I never had them before. I can't blame those readings on the MM because at the time I was was going from a 55g to a 120g so I was adding newly mixed water and live rock (cured but you really never know for sure). All that bio-load so fast, most likely was the cause. But I never really had a cycle, probably because of the new water. I would suggest keeping a close eye on your parameters. If they start to get out of your comfort zone, start doing waters changes until you notice things start to mellow.
All in all I recommend the MM. The only down side is it is very silty(sp), super fine. If you happen to stir it up, like accidentally drop a piece of rubble, instead of sitting it down softly, it can get into you display, making it a little cloudy. Still good stuff.
