I've set up our new 60L biorb tank about 4 weeks ago. Put fish in after a week or so only 3 platys at the mo. Used nutrafin cycle and keep testing the water every other day. Since last week nitrite is at about 7 I've done two 20% water changes which keep it at bay for a few days. No ammonia in water. Is the tank just going through this new set up nitrite spike I've read about?