Aquarium Cycling Without Killing Your Fish

Aquarium cycling is the most important part of setting up your freshwater aquarium.  You must keep in mind that it takes patience.  The entire process takes as long as 6-8 weeks.  Don’t worry.  We’ll get some fish in there before that.  I know you will be eager to fill your tank full of fish.  It’s only natural.  You just set up you new shiny fish tank and you want to see some fish!  What you might not realize is that adding the wrong fish, too fast is just a recipe for disaster.  You’ll quickly have a tank full of floating fish.  This can be costly, frustrating, but most importantly very cruel to your fish.  Aquarium cycling is really a very simple process if you keep in mind what I said before, patience.

There Is a Right and Wrong Way to Cycle Your Tank

Please resist the urge to cycle your tank using fish on the first day.  There are some sources out there that suggest this cruel method.  Even if hardy fish are chosen, introducing them this early in a new tank is VERY stressful on them.  The fish tank cycling method that I’ll describe is preferred by most aquarium hobbyist.  For your reading pleasure, I’ll do my best to save as much chemistry as I can for another article.  Alright, here we go.  We’re going to demystify this whole scary aquarium cycling thing.  Get your water chemistry test kits in hand.

Stage 1 – Grow Those Bacteria!

To kick off the bacteria maturation process, you’ll want to add an aquarium cycle starter like Bio-Spira, Stability, or Septo-Bac to your tank after you add your first round of water.  The point of this step is purely to grow bacteria.  Bacteria is necessary to change the ammonia produced from fish waste into nitrite, and finally into nitrate.  This fancy process is called bio-filtration.  Ammonia and nitrites can both be very harmful to your fish.  Nitrates can be harmful at very high levels but are comparatively harmless.  OK, that’s it for the hard chemistry, sorry.  You will want to let your bacteria mature and hold off adding fish for the first 2 weeks.

Stage 2 – Keep Those Ammonia and Nitrite Levels in Check.

Finally, it’s time to add your first fish! Yippee.  In step one you have established the bacteria that is necessary to process low amounts of ammonia.  However, there won’t be enough to process high levels which is why it is best to start with only one fish.  You will want to choose a hardy fish as your first fish.  A Zebra Danio or a Black Widow Tetra are suggested hardy first cycling fish.  You should allow at least one to two more weeks to monitor your water chemistry before adding another fish.  During this stage you’ll want to monitor the ammonia and nitrite levels to make sure they do not spike to harmful levels.  If your levels reach the harmful range you will want to do 25%-50% water changes as necessary to keep these levels in check.  I suggested doing these changes at least once a week.  You’ll want to remember that water changes are the best way to fix high ammonia, nitrite, or nitrate levels.

Stage 3 – Don’t Forget About That Nitrate.

By this time your ammonia and nitrite levels should have reached minimal levels.  This usually occurs about two weeks after adding your first fish, making it approximately four weeks into the cycle. Once your ammonia and nitrite levels are low you are ready to add a couple more hardy fish.  Your bacteria should be healthy enough to start controlling your ammonia and nitrate levels at this point.  Because of this, you can even add a couple hardy fish each week for this four week stage.  With the introduction of this number of fish, you will now start to see your nitrate level quickly rise.  Again you will want to do water changes of around 25% every week for another four weeks.  This time the changes are to control the nitrate level.  Don’t forget nitrate is virtually harmless compared to ammonia and nitrite.  The biggest problem with a high nitrate level is that it can cause unwanted algae growth. Alright, you did it!! This completes the full cycle of around eight weeks.  That wasn’t too tough.  You have now established a good bio-filter and can start adding more sensitive fish to your fish tank.

Don’t Forget to Balance out Your Water Temperature and pH

When you bring your fish home you should always first float the bag your tank water to balance the water temperatures between the bag and tank water.  This usually takes 15-20 min and is best determined by touch testing the two waters.  After five or ten minutes you will want to add some of the tank water to the bag to acclimate your fish to the pH level of your tank.

Tell us about your cycling story.