If you have zero nitrate your tank isn't cycled you will get ammonia first, ammonia will lower and you will get nitrite then nitrite will lower and you will get nitrate, you shouldn't do a fish in cycle with that many fish, are you doing the test on nitrate right by shaking bottle #2 vigorously for 30 seconds before adding the drops, also on the 1 min shake you don't have to go wild shaking it, a little hard but not hard enough where you're slinging water out of the tube, or get the tightest fitting cap you have.
It can take 2-6 weeks for a task to cycle, the process is slower with fish in as you're constantly changing water.
Feed lightly as well meaning don't over feed.
What filtration are you running on the tank?
Did you add the store water into the aquarium when adding new fish as you should never do this?
Do not touch the filters while you're cycling a tank as that's what the beneficial bacteria is growing on which helps complete the cycle.
You can buy biologically established sponges on
http://www.angelsplus.com/FiltersSpongeActive.htm
Your lfs might give you a bag of cycled substrate or media from one of their tanks.
I would go out and buy a bottle of stability which is live bacteria in a bottle, I would also modify the filter with media if it doesn't already have it I would increase the temp slowly up to 80 as bacteria grows faster at warmer temperatures, your fish will be fine at 80°, if you have an airstone turn it up on high.
Again don't touch the filters while you're in the process of cycling, just do daily water changes treated with prime, also know this you're still going to get ammonia readings with prime but it's actually ammonium (less toxic) that prime turns ammonia into.
