Cycling Your Tank or Aquarium

Cycling Your Tank or Aquarium

Cycling an aquarium tank is the process by which the plain water in the aquarium is turned into an environment which livestock is able to live, grow and thrive. This is true for any kind of aquarium, fresh or salt. Every aquarium must go through this process to be successful.
Just like you, little fishies and all the other livestock in the tank eat. And also like you, after they eat they have to go to the potty. Except, unlike you, (hopefully) the entire tank is their potty.
To take care of this, certain kinds of bacteria must grow in your system to counter the toxins that are produced in the tank. Unlike the normal bad name that bacteria generally get, these are ‘”GOOD” bacteria.The right bacteria must be cultivated in your filter system by allowing nature to take it’s course. Once your tank is fully cycled, your system will have the right biological and chemical balance for livestock.
Here are 12 points for cycling a tank:
  1. Basically, a new system starts out with no bacteria.
  2. Bacteria eat waste.
  3. To create bacteria, we have to create waste.
  4. To create waste byproducts (ammonia) add hearty livestock.
    1.   For saltwater aquariums, add uncured live rock.uncured live rock releases more waste and provides a place for good bacteria to grow. Some people use small fish or inverts,but using uncured live rock seems to cycle faster.
    2.   For freshwater use small fish to cycle the tank. Probably not a good idea to use expensive fish. Also you should not use aggressive fish as they will become stressed enough until the tank gets balanced.
  5. Ammonia is a byproduct of waste. Ammonia is deadly to livestock.
  6. You will see a high ammonia spike. This is great! That means cycling has begun.
  7. As the bacteria multiply in your filter system, they convert ammonia to nitrite. Nitrite is also highly toxic but not as deadly.
  8. Ammonia comes down, nitrite goes up.
  9. Bacteria convert nitrite to nitrate. Nitrate is the least toxic.
  10. Ammonia and nitrite comes down. Nitrate goes up.
  11. To get rid of nitrate, you must do a water change – no more than 20%.
  12. The end goal is ammonia at zero, nitrite at zero, nitrate < 30 ppm,  pH between 8.1-8.4, For salt try to keep your specific gravity between 1.020 – 1.025 . (specific gravity range varies slightly with livestock types SEE BELOW)

NOTE: Tank cycling may take 1-8 weeks.

Remember to add livestock slowly. As livestock is added, it creates waste which creates ammonia. You need to allow bacteria to catch up and multiply to keep your system balanced.


  • Live Rock Cycling: (Wikipedia: “Live Rock”)

    • Once cycling is complete and the live rock is cured, there should be no more die-off or smell.
    • Also, waste from your protein skimmer should be greatly reduced.
  • Salinity
    • Use an instrument called a hydrometer to measure specific gravity.
    • Salinity is the measure of total salts dissolved in water. Salinity has an indirect relationship to specific gravity.
    • Specific gravity should be between 1.020-1.022 for fish-only aquariums and 1.023-1.025 for reef aquariums.
  • pH
    • pH is the ratio between hydrogen ions and hydroxide ions.
    • The goal in saltwater aquariums is to have the pH between 8.1 and 8.4.
    • Over time, pH tends to fall due to natural processes. To prevent this drop, we must maintain the system’s alkalinity.
  • Alkanity
    • Alkalinity measures the buffering capacity of seawater.
    • Buffering capacity is the seawater’s ability to resist lowering pH caused by a natural process called acidification.
    • We measure alkalinity on the dKH (degree Karbonate Hardness) scale. dKH should be between 8 and 12.

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