Best to test the water BEFORE a water change. This will allow you to know what the levels are or were before the change that may have been contributing to problems.
Matter's little what the readings are AFTER but water change is always a good idea when fishes seem off.
Fishes could be spawning and so long as fins were not being torn or fishes were dying outright,I would not be too worried were it me.
Tetr'as don't gaurd eggs they simply scatter them among plant's and will turn around and eat them as well if they happen across them .
If your tank is large enough,,you could try adding another four or five or six more Bloodfins.
this should help any one or two fish from being singled out for chasing ,nipping.