well, i know that they have hang on refuge's (or fuges). They look pretty much like a hang on back filter, except they're quite a bit bigger. They also have a light on them, so that you can put macros in there. Macro is a type of algae...i think its kinda bushy lookin. Anyways, you put the macro in there, and when the water passes thru it, it takes in the nitrates. I think you also put live sand in the fuge too, but i dont have one on my tank (prolly gonna get one, but my nitrates are perfect right now) so i'm not sure about the sand part.
So I can leave tank without fish thorugh cycle?
yes, you can leave it with fish through out the cycle. put a couple of those dead shrimp in there to jump start the bacteria growing. (i think you can take those out after about a week and a half or so, but i'd wait for someone else to chime in on that). Also, if you can afford it, definately get at least 10 lbs of live rock. If you have enough live rock, i've read that you probably wont see much of a cycle, but i dont know if 8 lbs is enough.
anyways, the first thing that will happen for your cycle is the amonia will go up...i think anyways...thats what happened on mine.
Then, once your rock and everything gets the bacteria goin (your amonia will probably go back to 0 at this point)...it breaks the amonia down to NITRITES. At this point, your nitrites go up, and, same as with amonia, they get broken down (and go back to 0) and turn into NITRATES.
Nitrates, as we've said before, (and i found out!!) are non-toxic to the fish, but could kill inverts, and when they die, they DO create problems because they make for poor water quality. However, if you have the hang on fuge, with macro in it, then you shouldnt have any nitrate problems.
once EVERYTHING goes back to 0 you're done! Although there will probably be a few nitrates still, but anything under 15, you dont really gotta worry, but anything above 20, you should check to see whats goin on.
sorry for the novel, but HTH