Tank Cycling: How I learned not to kill everything I touched by John Harris (Aiptasia)

Welcome to the world of Aquaria. Try not to kill anything…..

That would’ve been sage advice to my nine year old self. I was standing in a pet shop, grinning from ear to ear with my prized winning goldfish from the ping pong ball booth school bazaar in my hand.

 The man in the pet shop sold us a ten gallon tank with some jungle brand dechlorinator, a corner box filter, some carbon, gravel, filter floss, airline and an air pump. He told me that the fish was called a comet goldfish, which became it’s name. Comet. Comet the fish. I set up Comet’s tank on my homework desk in my room at the time. After I’d set up everything in my new fish tank and floated Comet’s bag in the water for ten minutes, it was time to turn him loose. My new goldfish appeared to be happy in his home, free of the goldfish farms and overstocked tanks and now in a completely empty tank. All by himself. I was never so happy to have an aquatic pet. Something fascinating to watch, feed and interact with.

The next morning, I awoke and noticed something was immediately wrong with Comet’s tank. The water had turned cloudy, and poor Comet was gasping for breath at the top of the tank. I immediately changed 100% of Comet’s water in the tank, moving him to a small bowl while i did the water change. It was a Saturday, but I had a busy schedule with a lot of activities planned. I couldn’t fish-sit, so I did my best and changed the water out, scoop by scoop, with a pitcher i’d borrowed from the kitchen. After fresh and clean water was back in the tank, I released Comet from the bowl and back into his home. Concerned for my new fish, I left and went about the day. He looked happy. He wasn’t gasping any more. Whew. Close call. He’ll be fine, right?


Poor Comet. He was quite dead when I got home. R.I.P.. I sat there a sad child. Having to scoop up a dead fish and sacrifice him to the porcelain afterlife. This was my first pet that I had complete and sole responsibility for and it died. Dead. In my care. It felt horrible. My parents tried to console me by offering to take me back to the pet shop. In those days, pets like fish were seen as disposable. People didn’t know as much about caring for them and figured their deaths were a part of teaching children about nature. This was the 1970’s. Fish were seen as a baby step lesson for children about the great circle of life.

Maybe you’ve been here, too. You’ve faced your own new tank hurdles and remember them well. Maybe you’re new to aquarium keeping and would like to learn a few tips and techniques for where to begin. If you’ve ever lost your pets because of your new tank, did you give up on it or did you stick with it? I chose to stick with it, and while at the pet shop, was inquisitive enough to ask the pet store owner why my fish went belly up. He was the owner. He had to know more about fish than that salesperson last night.

"Young Man, what do you know about the nitrogen cycle? Don't you know that goldfish secrete ammonia out of their gills and poop a lot? I bet you didn't let your tank cycle, did you?"
Dude McDude
Pet Shop Owner

I’d learned a hard lesson…. I had to admit that I didn’t know anything about the nitrogen cycle, or that the filter I was sold wasn’t good enough to keep my new pet goldfish alive. I had no idea that I would be attempting to recreate an entire ecosystem in a small glass box. But, that is exactly what we are doing at home: Creating a complete environment for your living things to thrive in. To your aquatic pets, the inner dimensions of your fish tank is their entire universe. Fast forward four decades and here I am, over a hundred tanks later and i’m still in the hobby. 

So, what is this cycle and what’s so great about it? Well, we’re talking about the Nitrogen cycle, and it is perhaps the most important concept to understand when it comes to keeping aquariums. You see, fish eat food and that turns into fish waste (poop and ammonia). Uneaten fish food and fish poop decompose into water soluable molecules. The worst of which is ammonia. Fish don’t have to wait on anything to digest to produce ammonia, they secrete it out of their gills right into the tank water. Ammonia is quite toxic to fish, invertebrates and all manner of life. At high concentrations over .5 ppm (parts per million), the ammonia level can be deadly in your tank. That was the main reason I lost my pet goldfish, because goldfish in particular secrete an extraordinary amount of ammonia.

Luckily, there are beneficial bacteria that can use ammonia as a food source. They can actively consume ammonia and convert it into another chemical. This new molecule is called nitrite. Nitrite is equally deadly to fish and invertebrates, but thankfully there are different species of beneficial bacteria that can consume the new nitrite molecules. When they do this, the nitrite gets converted into a less harmless molecule known as nitrate. Fish are generally very resistant to nitrates however invertebrates and sensitive species like saltwater corals need to live within a specific range of nitrate (around 5-10 ppm). Nitrate can be further broken down into nitrogen gas through a process known as dentrification. We will discuss dentrification in a future article. The conversion process of going from harmful ammonia to much less toxic nitrate is known in aquaria as the nitrogen cycle. It could save your tank from disaster.

So, how do you get those beneficial bacteria to grow in your tank? Simple, you need to create a home for them to grow on. This is known as establishing biological filtration in your aquarium. It’s creating a home where your beneficial bacteria can colonize, grow and thrive in your tank. The quickest way to get them to grow in your tank is to pick out a filtration system that allows for simple biological media to be added to it. The type and style of biological filter will depend largely on the type of aquarium you wish to keep. However, once you have an established colony of beneficial bacteria, you should be able to create a less toxic environment for your pets at home.

How to cycle a tank without fish:

Simple. Fishless tank cycling is easier than you think. You don’t need fish to cycle your biological filter. You just need an ammonia source. If you can find a bottle of 100% pure ammonia (cleaning supplies stores), you can add a few drops to your tank at a time until an ammonia test kit reads .2 parts per million (ppm). Once your ammonia reaches .2, just leave your tank alone and let the biological filtration process begin cycling. There’s no need to continue dosing ammonia, just wait until all you can read with test kits is nitrate. Then, you can do a few water changes to lower the nitrate and your fish tank is cycled and ready for a few fish. You can also do fishless cycling with fish food, chopped clams or even a piece of shrimp as your ammonia source.

How long does aquarium cycling take?

Since these beneficial bacteria species are everywhere, it still takes time for them to grow. The usual length of time to cycle your tank’s biological filter is about six to ten weeks. Remember, you’re growing two different kinds of bacteria: Bacteria that eat ammonia & bacteria that eat nitrites. The ammonia eating bacteria always seem to grow in the fastest, followed by a long lag time until the nitrite loving bacteria grow. 

How can I tell if my aquarium is cycled?

There are test kits you can use to monitor your tank’s nitrogen cycling process. A lot of pet shops will also do simple water tests for customers for a small fee (sometimes free!). You can buy individual kits to test for ammonia, nitrite and nitrate or you can purchase a master test kit that has all of those tests, including other tests for various water parameters. Be sure to pick out either freshwater or saltwater test kits for more accurate results.

How to instantly cycle a fish tank:

You can’t, unless you have an alternative ammonia and nitrite consumer in your tank. The only fish tanks that can come close are very heavily planted aquariums. Fishless cycling with plants is possible if you fill the tank with live plants (Think Amano or Dutch Style planted tanks). Tanks of these two heavily planted with live plants will also cycle, but the plants will use the nitrogenous wastes as a fertilizer. There are various bacteria in a bottle style products, pre-inoculated filter media and aquarium substrate that make claims that they can speed up the nitrogen cycle. In my experience, it takes about the same amount of time either way. There is just no way to instantly cycle a fish tank. Patience is a virtue young grasshopper. 

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4 thoughts on “Tank Cycling: How I learned not to kill everything I touched by John Harris (Aiptasia)

  1. There is a way to drastically reduce the time to a cycled tank IF you have access to an already cycled tank with a filter of the same type of equal or larger size. Put your filter media in the established filter next to the established filter. Leave it there for a week. This will “seed” your media with both the ammonia-to-nitrite AND the nitrite-to-nitrate bacteria. This will speed things up considerably because it’s the nitrite-to-nitrate bacteria that takes the longest to start. Be careful to keep the media wet and warm, it IS somewhat temperature sensitive and absolutely MUST stay wet. It is also more sensitive to chlorine and chloramine than the fish. Used tank water from the donor tank is your best bet.

    This still won’t be an instant cycle, but it will reduce your time to 3 to 5 weeks(including the seed week), so about half the time.

    I’ve been keeping even longer than John, my first tank had a stainless steel frame and a slate bottom. Neither one of us had the advantage of the internet, we made a lot of mistakes, hopefully you can learn from our hard won experience.(Even after 40 to 50 years of keeping, we’re both still learning! Sometimes, even from “newbies”, lol!)

    1. AUGH! The new media should next to the the established filter’s media, INSIDE the established filter, not just next to the filter…

    2. Yep, that’s a good point and it’s a good idea to seed your new aquariums with a pre-cycled filter media. It doesn’t hurt to have extra sponge filters going for this purpose, but remember it’s only as effective as the current nutrient load. In other words, if you remove a sponge filter from an aquarium with two sponge filters cycled and going in it, you’re removing 50% of the bio filter from the old tank and the new tank’s bio load cannot exceed 50% of the previous tank’s bioload. That can mean an ammonia spike in the old tank AND the new tank if it isn’t done correctly. So, it’s tricky or at least it can be. My favorite trick for a new tank is to just squeeze the fool out of an old sponge filter into the new tank to mulm up the new filters. It helps.

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