Yes, they are raising their fry as we speak, and the exesive nitrates I contribute to the fact that I just fed them, with powdered flake food and it got a little messy. So danios? <aybe long finned? MAYBE GUPPIES?
Just fed food does not turn into nitrates that fast ...
If they're a breeding pair, I wouldn't add anything to the tank either. I would however do a water change pretty quick so the babies aren't choking on nitrates.