Something old- Something new...Reflecting upon the "aging" aquarium...what exactly is that?

As you surmise, I do get a lot of email and PM’s from readers of my ramblings here in "The Tint" and elsewhere, and I get some pretty interesting requests and questions, as well as suggestions about topics people would like to hear about. Today, we’re going to touch on a topic suggested by a reader. The request posed was to discuss the maturing process of a tank- specifically, thoughts on what the difference is between an aquarium that is just “cycled”, and one that is defined as “mature.” 

What an interesting topic! Of course, I’ll throw my two cents worth out there, and then we can all add to it and discuss..

I guess the logical place to start such a discussion would be…at the beginning. Well, the beginning phases of your tank, that is. You know what I mean: You’ve designed the perfect system. You spent a ton of money on the best filter you can afford, an insanely powerful LED lighting system, and you even settled on sexy schedule 80 PVC for your hard plumbing…This tank is gonna rock!

Of course, before all of the killer fish are swimming about peacefully and the plants settled into their new home, you need to “cycle” the system, and get it suitable for life forms to reside in. It’s one thing to have a nicely-equipped system, quite another to have a suitable system for aquatic life. It’s still another when it earns the lofty  hobby moniker of “mature.”



I am operating on the assumption (gulp) that most of us have a basic understanding of the nitrogen cycle and how it impacts our aquariums. However, maybe we don’t all have that understanding. My ramblings have been labeled as “moronic” by at least one fanboy- er, um, “critic”, however, so it’s no biggie for me as said “moron” to give a very over-simplified review of the “cycling” process in an aquarium, so let’s touch on that for a moment! 

Ammonia, nitrite, and nitrate…arghhh!

During the cycling process, ammonia levels will build and then suddenly decline as the nitrite-forming bacteria multiply in the system. Because nitrate-forming bacteria don't appear until nitrite is available in sufficient quantities to sustain them, nitrite levels climb dramatically as the ammonia is converted, and keep rising as the constantly-available ammonia is converted to nitrite. Once the nitrate-forming bacteria multiply in sufficient numbers, nitrite levels decrease dramatically, nitrate levels rise, and the tank is considered “fully cycled.”

So, in summary, you could correctly label your system “fully cycled” as soon as nitrates are detectible, and when ammonia and nitrite levels are undetectable. This usually takes anywhere from 10 days to as many as 4-6 weeks, depending on a number of factors. In my experience, there are certainly some “cheats” you can use to speed up the process, such as the addition of some filter media or substrate from a healthy, “mature” aquarium, or even utilizing one of the many commercially available “bacteria in a bottle” products to help build populations of beneficial bacterial populations.

So we have at least, for purposes of this discussion, established what we mean in aquarium hobby vernacular by the term “fully cycled.” However, what does “mature” mean? Well, here is where we lose some of the hard facts and get into judgment calls and opinion…and that’s okay. I’ll give you my thoughts on the topic, and I expect to hear yours!

In my opinion, a “mature” aquarium is a system in which the nitrogen cycle is fully functioning, and nitrate is regularly produced as the “end product” of the biological filtration process. However, it goes further than that. I believe that truly “mature” systems have several distinct traits that set them apart from newly-cycled systems, specifically:

*Significant populations of microfauna, algae, and fishes are in the system, with very few anomalous “crashes” or fish deaths occurring. Ammonia and nitrite are undetectable in the aquarium. Stability exists in terms of populations and environmental fluctuations.

*Rock and wood has some algae and other macro life in and on it. Stable populations of amphipods, copepods, and/or other small crustaceans are present.

*Fish population has been stable, healthy and consistent, with few losses with any frequency.

*Plants are actively growing and increasing in size as well as improving in health and color. 

What’s more, there is a certain “Something” to a mature  aquarium…A smell, a look, a lack of excess in either “good” or “bad” animals. In my opinion, a “mature” aquarium is one in which you don’t have to freak out every time you miss a water change, forget to feed, fall behind on algae scraping, top-offs, etc. Aquariums that are environmentally stable allow the aquarist a certain degree of latitude in maintenance and overall husbandry. But that doesn’t mean you can kick back, of course.

Mature tanks also can fall into what author/reef aquarium great/friend Mike Paletta referred to as “Old Tank Syndrome” back in 2006. Mike asserts (correctly, IMHO) that a (reef) system (and by association, ANY aquarium) is NOT a “slice of the ocean (pond/lake/river)”; rather, that it is a closed system, and is subject to accumulations of nutrients (specifically nitrogenous waste and phosphates) over time, many of which can reach a detrimental concentration unless maintenance is stepped up to combat their accumulation.

Regular, though not obsessive- water parameter monitoring is always advisable to ascertain just what is going on in the aquarium. We’ve talked previously about establishing “baseline” operating parameters for your tank, and trying to stay within that baseline for the life of the aquarium.

In other words, even with regular maintenance practices and monitoring in place, you can’t truly set the aquarium “on autopilot” and let it run itself. There is a constant “war” between good and bad chemical concentrations going on in your system, and you need to be on top of things in order to assure that the “bad” doesn’t outweigh the “good.” 

What this might mean in practice is that stepped-up water changes and other maintenance may be employed as necessary to combat excesses. How do you know that you have excesses of organic nutrients building up in your long-established aquarium?

Well, when you start noticing outbreaks of algae where none existed previously, that’s a tip off- as is the failure of previously thriving fishes or plants to display the growth and vigor they once did. Sure, a planted aquarium is a lot like a garden, and you’ll need to “prune” regularly to assure that plants  aren’t growing all over each other, disrupting water flow patterns with their growth, and smothering other plants. This “competition” is even more pronounced in a well established tank, where real estate is at a premium, and each plant is “looking for the edge” over it’s neighbors for space, nutrients, light, etc.

 The bottom line is that an aquarium, being a closed system, will demonstrate some characteristics that are easily identifiable when it’s “mature”, but that you still need to address all aspects of husbandry and maintenance throughout its existence. Much like a garden, an aquarium could “run wild” if left to its own devices, and the outcome for many plants and fishes in residence could be negative.

No one said the hobby is easy, but it’s not difficult, either- as long as you have a basic understanding of the environmental processes and conditions within your aquarium. 

I’d like to hear your thoughts on this topic. If you can offer personal opinions, examples, and experiences, this would be particularly interesting. I know it’s a topic that’s been kicked around before, but let’s bring it up again and share.

Thanks as always for your feedback!


Stay wet.

Scott Fellman

Tannin Aquatics

Scott Fellman
Scott Fellman


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