Cycling? What’s that, and what does it have to do with aquariums?!

That’s exactly what I thought, when I first started getting into the fish keeping hobby. In fact, when I jumped right into purchasing my first 10gal tank and several fish, I was hit with a bombshell of a surprise through several different people on aquarist forums, like Aquatic Community. To my surprise, the reason why so many people jumping into the hobby experience so many fish deaths, is because they hadn’t cycled their tank first. This was the moment that set me on the educational roller coaster ride of fish keeping, full of ups, downs, zig-zags, zen and fun.

Let’s clear some things up first…

If you were to define “aquarium cycling,” it would read something like this: the process of building a colony of beneficial bacteria in an aquarium for natural filtration of toxic compounds. Well, something like that.

To be more specific, however, it is the building of bacteria colonies which eats/oxidizes Ammonia (NH3) and Nitrite (NO2) – also called Nitrosomonas marina (the Ammonia oxidizing bacteria) and Nitrospira (the Nitrite oxidizing bacteria). It is often confused (and previously believed) that Nitrosomonas europaea is responsible for Ammonia oxidizing, and that Nitrobacter oxidizes Nitrites. These misconceptions have been disproved as late as 1998 and 2001, by Marine Biologist Dr. Timothy Hovanec, Ph.D. Cycling is also called the “Nitrogen Cycle,” due to the break-down and conversion of the element of Nitrogen (N) compounds

So, why is this necessary?

Well, as previously mentioned, Ammonia and Nitrites are quite toxic and very harmful to your aquatic friends. Ammonia is produced through waste products, such as fish pee and poop, the product of fish exhalation, and other decaying matter, such as dead leaves from aquatic plants and uneaten food. Nitrites, on the other hand, are produced after Nitrosomonas marina oxidizes Ammonia. The Ammonia is converted through the oxidization process into Nitrite. While this removes the toxic Ammonia, Nitrites are just another toxic chemical compound that can hurt and kill fish. That is when Nitrospira comes into play. The Nitrite is converted by the Nitrospira into a less harmful chemical compound called Nitrate (NO3).

While there are Nitrate eating bacteria, they are anaerobic (unlike their aerobic cousins mentioned above) and rarely colonized. If an aquarist were to go this route, they’d typically do so in a saltwater aquarium, where they would create a plenum or de-nitrating coil, which depletes a portion of the aquarium (usually under the substrate) of oxygen, where the Nitrate eating bacteria can flourish. Typically, our aquariums (especially Freshwater Aquariums) are highly oxygenated through the use of filters, air pumps, plants, etc. to create a healthier environment for our tank inhabitants, so it’s improbable without a lot of extra work/determination to colonize this hobby-rare beneficial bacteria.

So what do you do about Nitrates, if you have a freshwater aquarium and can’t build a plenum or de-nitrating coil?!

Don’t fall apart on me just yet! Just because you can’t build a colony of Nitrate-eating bacteria, doesn’t mean you can’t rid yourself, quite easily, of the toxic compound! Rest assured, it’s quite easy. For one, plants utilize Nitrate as a fertilizer. They absorb it as a nutritional substance. However, not all plants utilize the water column with the same efficiency. Some absorb a great deal of Nitrate (such as some floating plants, like Frog Bit and stem plants like Green Cabomba) and others only absorb a very small amount, like Amazon Sword Plants. Should you choose not to go the planted aquarium route (or you choose plants that aren’t heavy nitrate eaters), weekly water changes are the only method of reducing your aquarium’s nitrate toxicity.

See? Pretty simple. Your regular, weekly aquarium maintenance will take care of the toxins for you. And you’re already doing your regular, weekly maintenance, right?

“Ok, that’s great,” you’re thinking. So how do you colonize this bacteria?

Well, there are two methods. You can use the fishless method or the fish-in method. Historically, the fish-in method was looked at as the only way, but more recently the more humane (and faster) method of fishless cycling has grown in popularity. I’ve provided links below to the “how-to” for each method. Too much information on one page can be confusing for some, so I felt I should separate them.

Fishless Cycling
Fish-In Cycling

Ok, I understand the why and how, but what about the “how much?” How much? You mean, the necessities of having a bacteria colony large enough to handle your bio-load? Glad you asked!

Having a beneficial bacteria colony large enough to handle your bio-load is just as important as having one. The reason being, is because you can have mini-cycles in your tank, even if it’s cycled, should your bio-load change too much.

But first… what’s bio-load? Simply put, that constitutes the population of breathing inhabitants you have in your aquarium and the amount of waste (urine/poop/etc) they produce. Some fish have a smaller bio-load than others, and obviously, the more fish you have, the higher the bio-load. So, depending on your needs, the amount of bio-media you use will vary, and thus, the amount of time needed to populate that bio-media will also vary. Larger tanks typically have larger or more fauna, thus need larger filters, which in turn, require larger amounts of bio-media.

When you’re finished cycling a tank, there are usually two methods at which you can add new fish/inhabitants. All at the same time or only a few at a time. For instance, if you have a 10gal tank and are going to put in a Betta Splenda and 4 Otocinclus Catfish, at the end of your cycle, using 2ppm ammonia to cycle with a filter rated at 20gal, you could arguably add all of the fish at once. The bio-load for that tank size to fish ratio would be about average. If you were to cycle with the same filter, but only use 1ppm ammonia, you might add the Betta first, wait a week, so that more biological bacteria can grow and then add 2-3 Oto cats, wait another week and add the remaining stock. This process will allow your filter to play catch up with your tank’s needs. Adding more bio-load will sustain more bacteria. You just need to be careful about how you go about it.

Sometimes, a BB colony can crash if you lose some fish and don’t add any fish to compensate for a few weeks. The BB that you grew will dissipate, because the remaining bio-load can’t sustain them. Then, when you go to add more fish, you may end up with a mini-cycle, because your BB has to play catchup… but it can’t happen fast enough. This can result in seeing Ammonia and Nitrite appear again temporarily, and in greater number. If this happens, you need to stay on top of your water changes to keep the Ammonia <= .25ppm and your nitrites 0.

If you have any questions about the Aquarium Cycling process, please post comments below or contact me at the link above.

Thanks for stopping by.

-Kevin Bush