Before any aquarium can support livestock, whether fish or invertebrates, it must be completely “cycled”—another way of saying that biofiltration must be fully established in the system.
Sounds good, but what on earth does that mean? A system is considered cycled when it has been colonized by beneficial bacteria that convert deadly ammonia—produced through the waste and respiration of fish, the decomposition of organic matter (e.g., fish food), etc.—to less harmful byproducts.
One form of bacteria converts ammonia to nitrite, which is still deadly to marine livestock. Then, another form converts the nitrite to nitrate, which is relatively harmless in lower concentrations. Partial water changes must be performed on a routine basis to prevent nitrate from accumulating to harmful levels.
But how does the cycle get started?
Cycling is not simply a matter of allowing an aquarium to operate for some predetermined amount of time before adding fish or invertebrates. You can operate a new aquarium from now until doomsday (which, given the fact that Here Comes Honey Boo Boo remains on the air, is clearly close at hand) and get no closer to establishing a biofilter—unless you somehow introduce ammonia.
One such method is adding pure household ammonia (containing no dyes, perfumes, or other additives) or to the system. Another is feeding the tank—literally adding fish food on a daily basis and allowing it to decompose, thereby producing ammonia. There are also ammonium chloride solutions specifically targeted at aquarists.
In the past, it was common practice to add a few very hardy fish—typically damsels—to jumpstart the cycle with their waste products. This method is not only inhumane to the damsels, but also completely unnecessary when there are very effective “fishless” alternatives to cycling.
Live rock cycling is best
However, here at Saltwater Smarts, we encourage the concept of cycling with live rock, preferably the aquacultured variety. Live rock provides everything you need to get the cycle going in one convenient package, including:
- The beneficial aerobic nitrifying bacteria (live rock also contains anaerobic bacteria that convert nitrate to free nitrogen gas, but that’s a topic for another post)
- The perfect porous substrate to allow bacterial populations to flourish
- A built-in ammonia source
Ammonia from live rock? How so? When you introduce live rock to your system after it has been cured (that is, after the inevitable die-off of some encrusting organisms has been allowed to progress under controlled conditions), a limited degree of additional die-off will still occur. This additional die-back and subsequent decay will produce enough ammonia to get the cycle started.
What do I do during the cycle?
All you have to do is monitor the process with quality ammonia, nitrite, and nitrate test kits. As the cycle progresses, you’ll measure spiking and declining ammonia and nitrite levels followed by the appearance of nitrate.
How do I know when my tank is cycled?
When ammonia and nitrite are no longer measurable and nitrate is beginning to build up, the system is considered cycled and it’s safe to start adding livestock very slowly and incrementally.