Go online. API Master goes for around $20 which comes w/ pH, Ammonia, nitrite and nitrate. (it's been while, dont remember if comes w/ High Range pH too, not that you need). Meanwhile do small 25% water change and cut down on food until kit arrives.
If you go to Petco or another chain store I've seen them for up to $30. Sometimes I've found them at smaller stores for cheaper.
I'd say do a water change now and just keep watching the new fish. Sometimes it takes a couple days for them to get comfortable especially because you have zebra danios. They're quick little buggers... Your other fish just might not feel 100% comfortable yet.