What to Do After Your Aquarium Has Finished Cycling

saltwater aquarium

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Once your new saltwater aquarium has reached the third and final phase of the nitrogen cycling process and completed establishing the biological filter, it's important to be patient, and move slowly in adding more fish. 

The newly established nitrifying bacteria (Nitrobacter, Nitrosomonas and Nitrospira) that have developed need time to multiply. These bacteria are living entities that require oxygen to survive, and food (ammonia, which is primarily generated by waste from all things living in an aquarium). Living on the surfaces of everything in the aquarium, the larger their numbers, the better they are able to detoxify the wastes produced by the bio-load in the aquarium. However, when the bio-load "exceeds" the nitrifying bacteria population, ammonia will begin to increase in the aquarium again, and nitrite as well. Both ammonia and nitrite are toxic to your fish and other aquarium inhabitants.

Once your tank has completed its cycle, if you move too quickly in adding new livestock or overly disturbing your biological filter, you may experience a case of "new tank syndrome," so proceed slowly at this point.

Tidy up the System

Once the ammonia and nitrite levels have dropped to zero at the end of the second phase of the nitrogen cycling process, it's time to tidy up the system and get it ready for some new livestock with a few "light" cleaning tasks.

Light is the keyword here. Remember, the newly grown nitrobacteria that have developed in the final phase of the nitrogen cycling process are an essential part of building your aquarium's biological filter base. These beneficial bacteria live on all surfaces in the aquarium, and as they mature and multiply, they are what keep your system in balance. At this stage you do not want to strip them away and weaken their numbers, so here's what can be done.

  • Clean off the inside tank walls.
  • Remove any organic waste that has settled on the bottom of the aquarium by lightly siphon cleaning the "surface," and only the "surface" of the substrate.
  • Remove organic matter that has accumulated inside and around rock formations. This can be done by either squirting water into these areas using a turkey baster, or simpler yet, use a small powerhead. It's a great way to easily dislodge the gunk that gets trapped, releasing it into the water column where it can then be removed through filtration.

Perform a Water Change

In conjunction with tidying up the system once the ammonia and nitrite levels have dropped to zero, a water change can be performed. In the process of light siphon cleaning up the aquarium, old water is removed, and once done, you refill it with some new saltwater.

Doing a 20 percent to 25 percent water change at this point is beneficial for the following reasons.

  • It replenishes essential seawater trace elements.
  • It helps to correct and return changes in pH, salinity, alkalinity and other important parameters of the water to their ideal settings.
  • It improves the overall quality of the water.

Once the aquarium is cleaned up and refilled, it's time to rinse out any mechanical filtering materials, such as prefilter flosses, cartridges, sponges or pads. But don't clean them aggressively, as you don't want to lose the beneficial bacteria that grows on this media; just rinse off the solid debris that accumulates in the filter media.

Now let the filter system run for a few days to clean up the water. If at this point any prefiltering materials appear to be dirty, clean them again.

Tip: No water changes should be performed, or any ammonia destroying products added to the water while the tank is cycling, as this only delays and drags out the completion of the cycling process.

Add Some New Livestock

Once you have allowed the system to run for a few days after cleaning up the aquarium and doing a water change, test to see if the ammonia and nitrite levels are at zero, and the pH is correct. If any trace of ammonia or nitrite is still present, wait until they are gone before you add new livestock, and when all is ready, proceed, but only by adding a few things!

You don't want to overload the biofilter system. Otherwise, a spike in ammonia will likely occur. One or two primary diatom and macroalgae eating fish, such as Tangs, Angelfishes, and Blennies, as well as some snails, hermit crabs and other hardy tank janitors, are ideal additions at this point.

Stabilize the System

After you have added a few new additions to the aquarium, allow the system to run for several weeks to become stable before continuing.

This means you should test the water daily for traces of ammonia and nitrite after introducing the first new animals. The longer you let the system run before putting anything else new in, the better, because this allows the beneficial bacteria to mature and multiply, making the biological filter stronger.

When all looks good, go ahead and add a few more new livestock, as you did before.

Establish a Regular Aquarium Maintenance Routine

The key to keeping an aquarium in prime shape and having a happy fish or reef tank community is to take care of it on a regular basis.

Of course, there are some simple daily procedures that all aquarists should practice, but unfortunately, there is no set structure for doing other weekly, bi-weekly, monthly, or longer in between maintenance tasks. No two aquariums are set up or run the same, and everyone has an opinion as well as a reason for what, when, and how often any particular task should or may need to be performed.

We can provide you with some maintenance procedure guidelines, but only you can determine what and when certain things need to be done. As time progresses and your tank matures, you will come to know your system, and from this, you will develop a routine that fits your aquarium's individual maintenance care requirements.