I am fishless cycling two tanks, 75 and 55 gal. I started the cycle (with Bio Spira) 5 days ago. The 75 is starting to show nitrite, around .25-.5 ppm but the 55 gal is not showing any readings of nitrite. Is it a possibility that my 55 gal might spontaneously start spiking nitrite? is that normal? Or is something not going right in that tank?