I just bought my 10 gallon tank last night and I have the filter set up and everything and I am putting the water in tonight and putting maybe 4 zebra danios in tonight to help it cycle. How long should I wait to add more fish in it???
a while. the first thing is to monitor your ammonia levels and do water changes as needed to keep it below 0.5ppm. eventually (it took about 2 weeks for me in a 29g tank) your ammonia will drop off and show up as 0.0ppm. then you will need to be testing for nitrites and keep an eye on those, doing water changes to keep that under 0.5ppm. once your nitrites drop to 0.0 (another 2 weeks for me), check ammonia again to make sure it's still at 0. if it is, then get a nitrate test and wait for it to get around 10ppm or so, then do a 50% water change and you should be ready. search the forums for the word "cycle" or "cycling" and it may explain it better.
however, considering that danios like a lot of room to swim I'm not sure I would reccommend getting and more unless you get some cories or other kind of bottom feeders. don't get them until your cycle is finished though fishy cycling is a pain in the butt (I just finished one myself) but once you start one you gotta see it through.