trillyen,
I am going to take a stab at your question; although, I am still relatively new at this hobby (I bought my first marine fish one year ago today). Hopefully someone else will jump in if I get anything incorrect.
It is my understanding that our QT setups do not have enough of a biological filtration to totally control ammonia, nitrites and nitrates. We use a seeded sponge to help control these, but to keep the levels in check in the QT, frequent and large water changes are required. Without the liverock, macro-algea etc. there are not enough of the beneficial bacteria to control ammonia, nitrites and nitrates and I do not believe the QT will ever truely cycle and stabalize such as we see in our display tanks. The water changes are the key to keeping the parameters at a level safe enough for the fish in the QT.
By the way I just want to say I really respect the way you are going about this. You are taking the time to learn and listening to the people who offer you advise here. Unfortunately, too many people post good questions here, get good advise from the knowledgable folks on this forum and then they seem to ignore it and just go out and buy the "miracle cure" from the LFS.
To quote my Weight Watchers leader the only "miracle cure" is salt water. Sweat, tears, and the sea. Sweat represents the hard work we put into obtaining our goals, tears of frustration when things don't go right and tears of hapiness when the do go right and finally the sea which represents relaxation. We are fornuate in this hobby to have a bit of the sea in our house, nothing is more relaxing than to sit in front of our little pieces of the ocean, for hours, and whatch all of its inhabitants (even those little inhabitants that can only be seen with a flashlight on a sleepless night).
Now while I degressed there for a moment
my point is I believe the only cure for your QT is salt water. I pretty much keep a fresh batch mixing the whole time I am running my QT with a fish in it. When I see any traces of ammonia, nitrites or my nitrates are getting too high (fish are ok with a bit of nitrates) then I do a large water change to bring the levels down.