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Cycling Your Aquarium - For Dummies!

Where do you find fish in the wild? Oceans, lakes, rivers and streams. Are these sources of perfect, life thriving, crystal clear, pure water? Absolutely not. Life isn’t clean, it doesn’t thrive in crystal clear water. What keeps the fish alive and happy is a successful ecosystem of life on many levels. You’ve got the main fish of course, but crucially, and what our main topic today will be, you have bacterial life. Beneficial Bacteria isn’t just for the health of your digestive system, as a popular yogurt drink would have you believe. It should also be in your fish tank. Today we’re breaking down what this means as we discuss Cycling Aquariums (For Dummies).



The Overview

Let’s start right at the beginning for this, before you’ve bought fish. We can’t stress this enough, do not put fish in a brand new fish tank. The tank needs to be cycled first. Cycling a tank is also known as establishing a nitrogen cycle. Just like in the wild, you need that beneficial bacteria to build up so that it can tackle the nasties your fish leave behind… from their behinds.


The nitrogen cycle starts with fish waste, or ammonia. Ammonia is toxic to fish, so levels need to be kept down to maintain a healthy environment for them - the more fish you have, the faster this level of ammonia will rise. But how do you combat ammonia? You turn it into something else.


Over time, around 3 to 4 weeks, the ammonia in your tank will start lowering - this is down to bacteria forming which digest the ammonia and convert it into nitrites. So if your tank is capable of breaking down ammonia then you’re all set right? Not quite. Nitrites are also lethal to your fish. After a couple of weeks of bacteria building up due to the tasty and excess amount of ammonia in your tank, you’ll establish a colony of bacteria that love to eat it up and turn it into nitrites.


As the levels of ammonia lower and the nitrite levels raise, you’ll also develop colonies of bacteria that like to eat nitrites too! As these bacteria buddies build up they’ll lower your nitrite levels and convert them into nitrates, which are still bad for your fish, but not as highly deadly.



So in essence you go from a tank full of ammonia, to a mix of ammonia and nitrites, to a mix of nitrites and nitrates, to a tank full of nitrates. So what happens when you have the tank full of nitrates? Well unfortunately this won’t get eaten up by bacteria, this level requires some intervention. Namely, a partial water change. When nitrate levels get high, you’ll want to tip out some of the water in your tank and dilute it with fresh, clean water to dilute the nitrates.


Basically, by passively growing bacteria in your tank, ammonia becomes nitrites, nitrites become nitrates, then you keep the nitrates in check by diluting them with fresh water. With that being the basic process, let’s dig in a level deeper and look at levels.



Monitoring Your Water Parameters

You monitor levels by performing water tests with a Water Test Kit. The only test kit we suggest you opt for is the API Freshwater Master Test Kit (or saltwater if you’re going for a saltwater tank, bare in mind these are harder to maintain than freshwater). These kits come with test tubes that you fill up a little with your tank water. You then add a few drops of chemicals from the test solution bottles in the kit. The water in the tubes will then change colour, the strength of the colour indicates the level of chemicals in the water. For example, a slightly yellow colour will indicate a small level of chemicals, whereas a stronger yellow colour indicates a higher level of chemicals. The colour will match the test indicator sheet you get in the kit which is shown in a gradient of light to deep colours for each of the tests, as well as indicating the strength of the chemicals they represent in ppm, or parts per million.


So again returning to the start, your tank needs to contain ammonia, which is typically what fish waste becomes. However if you don’t have any fish in the tank, how do you get the ammonia? You add it yourself. Relax and pull your trousers back up - you can buy a handy little bottle of it! We recommend Dr Tim’s Ammonium Chloride Solution - this will give your tank its first boost of ammonia and kickstart the cycling process. Products like these either have you dump a whole lot of ammonia in at the start and let the process churn away, or they ask you to add some gradually as the cycle progresses. We’d suggest the second option so that you don’t create a vast amount of bacteria because of the massive amount of food which then runs out quickly, killing the bacteria. By adding it gradually you develop a constant, steady stream of bacteria that churns out the nitrites and then the nitrates.


You should use the Master Test Kit weekly to keep an eye on your water levels. Obviously at first you’re going to get a huge spike in ammonia - this is normal, as you’ve just added it to the tank. After a few weeks it’ll drop slightly and nitrites will rise, and then nitrites will spike and ammonia will drop. After this your nitrites will drop and nitrates will rise quicker, however your nitrates will be rising continuously as the first few bacteria ahead of the curve start to convert everything, so it’s also normal to have nitrate spikes while you’ve still got high levels of ammonia or nitrites - this is when you do a water change. Only change up to 30% of the water, you’re diluting the water - not replacing it. By replacing all the water you’ll remove the beneficial bacteria and your tank will have to restart the cycle.


Let’s dig in a little deeper now and discuss the actual ppm levels you need to keep an eye on. This level is pretty easy really as the ammonia and nitrites will eventually take care of themselves. What you’re aiming for here is complete removal of them - 0ppm. Less than 5 is what we’d call mandatory but it’s best to just wait until it’s all gone to start adding fish. Now obviously you can’t always keep Nitrates at 0ppm, and as they’re less toxic to your fish, you don’t have to! Less than 30ppm on nitrates is okay, once it goes over 30ppm, conduct your partial water change. Test weekly to make sure you’re getting into the swing of things in keeping on top of your levels. If you forget here it’s not a total failure - you shouldn’t have any fish at risk right now but it’s good practice to get used to your weekly fish tank test. As a hard level, 50ppm becomes dangerous for your fish, you shouldn't ever reach this point.


Typically, cycling takes about 8 weeks from new tank to cycled tank, however this can be sped up. Step one for the speed up process is using Dr Tims Ammonium Chloride, we’ve seen reports of it cutting this cycle time in half and it’s with Dr Tim’s mix in particular. Step two is to add live plants. You’ll need a plant substrate for this unless you’re using moss or floating plants, but plants naturally take in nitrites and use them as building blocks in their growth, this will cut a little of the strain on your bacteria for reducing nitrites and give your tank a head start for this step.



Step 3 is to increase the heat. Heat is a catalyst, it promotes quicker reproduction for your bacteria and since the end goal is to have tons of these bacteria swimming in your tank, it only makes sense to help them reproduce as quickly fast as possible. During your cycle, it is best to have the tank temperature somewhere around 83-87°F, any warmer and you could risk messing up the cycle. Also, I know we’ve mentioned this a few times but make sure you do not have any fish in your aquarium if you plan to use this method. Temperatures this high can be very dangerous for certain types of fish.


Step 4 - more oxygen. Your bacteria thrive on dissolved water, as well as ammonia and nitrites. You can help them reproduce quicker by also adding an air pump to your tank - something you may already be planning to do for your fish. We recommend this Hpumps Air pump, it’s efficient, is great for energy consumption and it’s very quiet.

Step 5 - Run your filter. Whether you’ve got an under gravel filter, a sponge filter, a submersible filter, a hang on the back filter or an external canister filter - you’ll want to get this up and running. The bacteria you need in your tank mainly house themselves within your substrate and your filter. This is also a great time to mention that when conducting water changes, never rinse your gravel or filter in fresh water - you’ll remove the bacteria. Instead you can squeeze your filter in some tank water you’ve removed from the tank. This will remove the bigger parts of old food and fish waste but will keep your bacteria. For your gravel, use a gravel vacuum to remove the dirt while maintaining your bacteria colonies. That way your substrate never has to leave your tank.



Step 6 - Turn off the lights. I know this will seem like a strange request and it’s tempting to keep your light on to witness the beauty of the tank you’ve lovingly prepared for inhabitants, but light inhibits bacteria reproduction, even when the fish are in your tank it should only be on for up to 12 hours a day. You’ll also want to keep your tank away from windows as the natural light will inhibit your bacteria colonies as well.


Step 7 - This won’t apply to most tank owners reading this guide, as it requires a cycled tank already. Step 7 is to transfer the filter media from an established tank. Now there’s two main ways you can do this, either install the new filter you’ve bought for the new tank into an established tank, so that the established tank has two filters. Leave it for a few weeks and it’ll fill up with bacteria, then quickly transfer it to the new tank - be careful to not let it dry as this will kill the bacteria.


The next option is applicable if you’ve got a sponge filter like the one shown below. These filters come with two sponges per filter - if you buy more than one filter this means you’ll be able to swap a single sponge from the established filter and swap it with one of the sponges of the new filter, so that each filter has one new and one established sponge.

The last point here is a kind of bonus point, it’s not essential and not really part of the cycling process itself. However, buying a bigger tank than your fish require will be one of the best investments you can make for tank maintenance.


The first point is that it’ll give you a bunch of space for your fish to play in, making them happier overall.


The second is that it gives you more space to add live plants, these will help you keep on top of nitrites and nitrates by using them as food to grow. This means you can go longer between water changes depending on how many you add.


The third is that there’s just more water in there. Build ups on nitrate will be slower because you’ve got more water to dilute them, but it’ll also mean that water changes are much more effective. If you’re thinking of a 20 gallon tank but go with a 45 gallon tank, then a 20% water change in the 45 gallon tank is more than twice as much fresh water for your fish as the 20 gallon tank.

In conclusion:

  • Opt for the biggest tank you can afford in terms of both money and space

  • Add your filter, an air stone and your substrates

  • Add live plants (planted ones require their own substrate/soil, floating plants and mosses you can add after adding gravel)

  • Add some ammonia

  • Turn up the heat

  • Turn off the lights

  • Test Weekly

  • When nitrates reach 30ppm, change 20% of your water

  • Wait for ammonia and nitrite levels to reach 0ppm

  • Add fish

  • Enjoy being a fish keeper

  • Continue testing and changing water (test weekly, change when nitrates reach 30ppm)


Thanks for reading our in depth guide on how to cycle your fish tank!


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The Ultimate Guide to Setting up and Cycling your Fish Tank



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