testing nitrate is tough. If you don't have ammonia or nitrite, you're fine. The nitrate test liquids have a low shelf life and the second bottle needs a really really good shaking. But don't worry about it if your tank has been running for that long and you rinse your filter pads correctly (shaking them in old tank water, do NOT run the pads under tap.)
I'd take back the zebra danios. they need to be in a bigger group and they prefer 4 feet of swimming space. Try for some harlequin rasboras or something of that sort instead. What are your tank dimensions? It seems like having 2 Bn plecs rather than one is kinda over kill. They're messy fish, without a doubt, and they can get significantly large.