LeighMo wrote ...

It might be best to just let the tank alone. Let the biological filter
re-establish itself, and the problem may go away on its own.

Or temporarily add several bunches of hornwort or duckweed or cheap stem
plants like pond penny and two teaspoons per gallon of A.C.T. by Markel.

My 2 cents U.S.,
kush

"You can't have everything - where would you put it?"