the presence of NO2
may suggest your tank's biological filtration cant keep up with the added bioload. In essence, a "mini-cycle" may be taking place. Any detectable NO2
is toxic to fish and especially inverts. Consider doing a large water change using aged SW
to pet parameters back in order. As far as feeding goes...this is a common avenue for NO3
to make its way ito the tank. Over-feeding can also cause a mini-cycle as the tank cant process the decaying food effectively. Light feedings every other day is plenty for most livestock.