Cycling A New Freshwater Aquarium


  1. A tank does not start cycling until there is some organic waste to work on.  There is no reason to run a tank with nothing in it for any length of time other than to make sure the temperature is holding and the tank doesn’t leak.
  2. Starting fish load: 1/5 to 1/10 of the tank’s eventual fish load.  This is about 4 neons, or 2 platies, or 1 gourami/ small cichlid, per 10 gallons.  Live plants: no limit; the more the better!
  3. Starting fish selection: Most fish are fine for cycling, but there are some that are too delicate.  Usually these will be marked with a RED border on their price tag; they include cardinals, rummy nose, hatchets, clown loaches, rams and discus.  Don’t bother with algae eaters; there is nothing to eat yet.
  4. Bottled bacteria: Purchase your favorite brand and READ THE LABEL.  Each type has different dosing instructions, and some are very different!  A tank will cycle with or without bottled bacteria, but it will happen faster with it.  It still takes time – there is no such thing as instant cycling.  Safe Start or Stability are recommended.
  5. Time to cycle: without bottled bacteria, typically about 30 days but can be as long as 60.  With bottled bacteria, up to 7 days.  Each tank is different.  You only know for certain by testing ammonia and nitrite.
  6. During the cycle: Do NOT add more fish; even if some die don’t replace them.  As nitrite rises gradually, fish can change their blood chemistry to adapt and survive, but fish suddenly exposed to the same high nitrite level may die.
  7. During the cycle: feed only once per day, to keep the waste load down.  Water changes may or may not be necessary during the cycle, but it can’t hurt to do them.  For peace of mind we recommend checking ammonia and nitrites daily during the first week and weekly there after.
  8. After the cycle:  A tank is cycled when Ammonia and Nitrite have returned to ZERO  (not “almost zero”).  Now you can increase feedings to twice daily, and can begin adding more fish.  Add a few every week, not a whole bunch at once (exception: African cichlids may need to be added in large groups to reduce aggression).


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