Totally agree with KK. What the shop is hoping is that you don't know -anything- about cycling and will kill a few rounds of fish and keep buying more at their shop. (I'm exaggeratng but you get the picture - it's become gradually built in to the subconcious business model of the retailers and no small part of it is that the customers themselves are going to naturally tend to the lazy side - but that's another story.)
When the shop says danios are good starter fish, the assumption is that you're going to use them as an ammonia source prior to being cycled, thus probably exposing them to gill and nerve damage, not to mention never even thinking about the swimming room they like. No, the kind of help you'll get here like KK is giving you is light-years beyond the often uncaring mentions from the shop.
-wd-