You basically have two options, but before i start i'd like to explain some things...
A nitrate reading of 10ppm is fine, as mentioned before readings up to 30-40 are common in some situations. The real danger to your fish is ammonia and nitrITE, its these things that kill your fish not nitrATE.
Anyway you basically have 2 options...
Option 1) Add your 6 danios into the tank just now. This is known as cycling with fish. Just make sure you change about 20% of the water every few days and top up with dechlorinated (sp?) water. This method endangers the fish in the tank as ammonia and nitrite will become present in the tank after about 1 week, maybe less.
HOWEVER many people have did it this way, just be prepared to lose some fish and keep up with the water changes and your tank should be fully cycled in around 2 months at most. Again this could be less but because your cycling with fish and doing regular water changes it will take longer to cycle.
Option 2) Dont add any fish into the tank for the time being. This is known as fishless cylcing. Get some pure ammonia from a hardware store (its a cleaning agent) and add enough to get an ammonia reading of 5ppm. Every few days check your ammonia readings and top it up to 5ppm as required. After a few weeks you'll notice your nitrite level begin to rise (good sign). Eventually your ammonia will read zero (good sign) and your nitirate level will sky rocket. Once this happens your tank is cycled. Complete a large water change (75%) and then add your fish.
This method does't harm any fish and generally take less time. But again this largely depends on the tank setup and water conditions.
So buy test kits for Ammonia, Nitrite and Nitrate if you dont alreay have them. And chose your method.
I've probably missed a few key points out but it can all be found in the sticky topics at the top of the beginners section.
Goodluck.
Paul.
