How to cycle a tank and get it ready for your fish

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How to cycle a tank and get it ready for your fish

So, seeing as we're Fully Cycled, we thought we should probably have a post about how to know if your tank is cycled, Fully Cycled if you will.

This post will cover how to go about cycling your tank but in a future post we'll also go over the common problems which can happen during the cycling process.

Now if you go into most local fish stores, they'll normally sell you some Seachem Stability and Seachem Prime. Now, this stuff is awesome, you put the right amount of Stability in daily and then put the Prime in every other day for a week and boom, you're done. Except, not quite. This is the start, at that point it is safe to add fish, but you can quite easily get spikes of harmful chemicals if you add too many fish or overfeed your tank. Especially during the first 6 or so weeks while your tank is getting established (cycling). So this post is going to go into the details of what we mean when you "cycle" a tank and so that if any problems happen, you will be able to figure out the solution and hopefully fix it, rather than just relying on different expensive Seachem products to sort it out! (we're using Seachem as an example but there are plenty of other companies that offer a similar thing!)

The Nitrogen Cycle

This is what we're talking about when we're asking if our tank is Fully Cycled, the nitrogen cycle is the process of turning Ammonia (Toxic) into Nitrite (Also Toxic), which in turn goes into Nitrates (Less Toxic).

But where is this Ammonia coming from? Well, that will mainly be from your fish, all that peeing and pooping that they do, that's one place, any food that's not eaten, that's another, but its not just the fault of your fish, your aquarium plants starting to die, that's another source. So as you can tell, there are a lot of reasons for a build up of Ammonia, and if you're not careful, Ammonia can quite easily kill your fish.

So how does that get turned into Nitrites? Well, Ammonia is turned into Nitrites by bacteria called Nitrosomonas if you have an Ammonia source in your tank then these little bacteria will thrive, they'll start to break down the Ammonia, essentially eating it and turning it into Nitrites.

Yay? No, Nitrites are still toxic unfortunately, but that's where our next bacteria come in handy. Nitrobacter breaks down the Nitrites into Nitrates, and that is the nitrogen cycle.

That bottle of Stability that the fish store sold you? It contains helpful bacteria like the Nitrosomonas and Nitrobacter which help quickly establish your tank.

So I can relax now? Yes and no. Nitrates are still toxic to your fish, just no where near as toxic as Ammonia and Nitrites. While Ammonia and Nitrites you want to keep at 0 ppm (parts per million) Nitrates can go up to about 20-40. To test this we highly recommend you pick up an aquarium test kit, while you can use test strips, they tend to be a lot more expensive in the long run and tend to be a lot less accurate.

There are 2 methods to lower the Nitrates in your aquarium, you can do a partial water change, 20-50% every 1-4 weeks (as and when your Nitrates hit dangerous levels) or you can add aquarium plants, plants will eat up these Nitrates as fertiliser, that isn't to say that you'll never have to do any water changes, as chances are, your fish are going to be producing more waste than your plants can soak up, but they can help extend the time needed between water changes.

So how do I cycle my tank?

Now that the science is out of the way, we can talk you through how to go about cycling your tank. There are 2 main methods, a fish-in cycle and a fish-less cycle.

Cycling with Fish in the tank

Let me start by saying this is not what we recommend, as it puts undue stress onto the fish which can cause illness and even kill your fish and should only be used if you cannot do the fish-less cycle.

The hardier the fish the better, a good example of a hardy fish is a guppy. These produce a ton of waste and can survive in harsher waters than most aquarium fish. We recommend 1-2 fish per 40 litres or so (10 gallons) as adding too many can lead to a spike in Ammonia levels and kill your fish before you even have a chance to react.

Once the fish are added, only feed them a moderate amount every other day, the reason for this is that the more they eat (or don't eat!), the more waste they produce which again, can lead to an Ammonia spike.

You'll need to do more regular water changes as well, we recommend doing a 10-15% water change every other day, this ensures you're not removing too much Ammonia that the growing bacteria is trying to feast on but also keeping it low enough so as not to kill your fish. Make sure when you add the new water you're pre-treating it with dechlorinator (or using dechlorinated water in the first place!) as adding chlorinated water will kill off all the helpful bacteria and ruining the cycling process.

We also recommend you're testing your water every 2-3 days for Ammonia, Nitrite and Nitrates, you'll see the Ammonia and Nitrite levels start to rise after the first couple days, as long as you're following along correctly, once both the Ammonia and Nitrite levels reach 0ppm, your tank is finally, Fully Cycled.

So now what? Can I add more fish? Yes, but slowly, the bacteria has build up enough to support the 1-2 fish you added, add another 1-2 fish then test the water again after a week, if the Ammonia and Nitrites are still 0ppm, you can add more fish. Keep up this process until you have your desired amount of fish but ensure you do not overstock your tank!

Cycling without any fish in the tank

This is the preferred method for anyone in the aquarium hobby, there are no fish in the tank to put any undue stress on and the most humane way to do it.

But without any fish how do we get the Ammonia we need to build up the bacteria? Simple. Add about as much fish food as you would normally feed your fish into the tank every 12 hours or so, if you're unsure, add a small pinch of food.

Test the water for Ammonia every couple of days until you see the levels sitting at 3ppm, at which point you can stop adding the food. Keep testing every couple of days and if the levels drop below 3ppm, add some more food in. Do this for atleast a week.

After that first week, you should start testing for Nitrites, once you start seeing Nitrite levels in your tank, you know the cycling process has started, keep adding the flakes and testing for Ammonia.

After a couple of weeks, you should notice the Nitrite levels start to fall, its at this point you can start testing for Nitrates, when you notice this, its a signal the cycle is almost complete.

Keep testing until the Ammonia and Nitrites are sitting at 0ppm, congratulations, your tank is Fully Cycled, make sure your Nitrates are below 40, if not, you'll have to do a partial water change to bring those Nitrates back to acceptable levels. Note that this entire process can take 4-8 weeks! 

So now I can add fish? Yes! But the same as the fish-in cycle, add slowly, and keep testing each week to make sure you haven't overloaded your tank. It can also be a good idea if you have any substrate to give it a good siphon to ensure that there is no trapped decaying food waste which could cause an Ammonia spike if released.

4-8 Weeks!? Can I not speed this up?

Yes, there are things you can do to HELP speed it along, there is no magic potion that'll instantly cycle your tank, if there was, we wouldn't need to write these big articles on how to do it! Here are our 4 methods.

1. Use media from an already established filter

This one is pretty simple, but not really possible if you're setting up your first tank. Most of the helpful bacteria will live on your aquarium filter media, so this one is easy, if you've already got a tank setup which has media in its filter, take some of it out and use it in your new aquarium.

2. Add your new filter into an already cycled aquarium

As above, this one isn't really possible if you're setting up your first tank. This method involves putting your new aquarium filter into an already established aquarium, simply let it run alongside the existing filter for a week or so and some of the helpful bacteria in that tank will nest itself onto the new filter.

3. Live Plants

Live plants will help introduce bacteria to help the whole process along, especially if you're sourcing them from an already established tank. These will also help bring you're Ammonia levels down quicker if you're using a faster growing plant.

4. The Chemical Method

Now this isn't something we suggest to keep up long term, its expensive and will break the bank! We mentioned this at the start of the post about fish stores selling you Seachem Prime and Stability. The Stability contains bacteria which will help kickstart your tank and should make the cycling process happen quicker, the Prime is essentially an emergency solution, it binds to the Ammonia and Nitrite in your tank essentially making it less toxic for 48 hours so that the bacteria can continue its Nitrogen cycle. So with this method, you do an initial dose like we explained at the beginning of this post, then every 48 hours add more prime. You will still have to do water changes when the nitrate levels get too high but it can be a helpful stopgap to keep your fish alive if something goes wrong. Note however this isn't always the case, as Seachem themselves say they don't know how it works, it just does!


Now, we know these above methods might not be for everyone but that's the only options we have really, there is also a downside to using the above methods as well. Any sort of nastiness that could be lurking in those established tanks could quite easily make its way into yours. This could be anything ie parasites or harmful bacteria, if you don't know for certain that the tank they have come from is safe, don't risk it!

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