Cycling your aquarium

The first thing you should learn about keeping fish is cycling your aquarium. Once you understand the basic idea it will be the single most important piece of knowledge that helps you keep your fish alive.

Most newbie fish keepers learn about cycling after they have set up an aquarium with fish that have died. Only then will they pick up a book to see why their fish died. That is a lesson they will not make again when they read about cycling.

mature cycled aquarium

mature cycled aquarium

1. What every new fish keeper must learn

Fish live and breathe in water. They urinate and poop in the water they breathe. Only one thing can stop them polluting themselves and that is bacteria that eats fish waste and converts it to the relatively harmless fertiliser, nitrate.

Your job as a fish keeper is to grow and keep alive a colony of bacteria that will clean the fish’s water. That is the secret to keeping fish alive for any length of time.
When you add fish to a new fish tank the water is clean. But day by day the fish’s waste product will build up because there is no colony of bacteria to digest the fish waste.

2. Emergency cycling

This is where there is fish in an aquarium and there isn’t a colony of bacteria that can convert the fish’s waste product into nitrate.
This usually occurs when a new tank has been set up and stocked with fish. It can also happen when chemicals or medications have been added to the aquarium which kill off the beneficial bacteria in the filter. It can also occur when the filter stops working, such as when the pump stops working or the filter gets clogged up with gunge. In these situations the bacteria die off and stop converting the fish waste.
Sometimes even when there is a bacterial colony in your filter, there can be an overload of fish waste or a source of decay such as rotting food or a dead fish. Or you might have an overstocked tank, such as when you have just bought some new additional fish or your fish have outgrown the tank or even when your fish have bred with many new baby fish overcrowding the tank.

The question is: How do you deal with this situation?

You need a nitrite and ammonia kit that measures these chemicals coming from fish waste decay. When the reading for ammonia is above 0.25ppm or nitrite above .5ppm then you will need to do a water change with water that has been dechlorinated with a chemical you can buy from the aquarium shop. The closer this reading is to 0ppm the safer it is for your fish but the longer it will take for your filter to develop enough beneficial bacteria. To reduce the amount of ammonia produced by your fish, you need to reduce how much you feed your fish and even stop feeding them for a day or two.

Adding aquarium plants can also help this process because they can actually eat up the ammonia. And usually plants have beneficial bacteria around their roots that will help speed up the the colony in the filter becoming established.

If you have a fully stocked tank with high ammonia levels then you could also try moving some of the fish to a second aquarium.

If you have another aquarium or a friend with an established aquarium then you can squeeze off the sponge (which is full of the beneficial bacteria) from that filter into the new tank. This will make the water cloudy but the filter will draw in the cloudy water with the beneficial bacteria. You will see clean water after a few hours. And with good luck the filter may mature within a couple of days.

3. What is cycling

Cycling is the process where an aquarium develops beneficial bacteria (unsually inside the filter) that breaks down the fish urine and poop into a fertiliser called nitrate. Fish waste products break down into ammonia. The beneficial bacteria eat the ammonia and convert into nitrite and then nitrate. In a new aquarium there is very little bacteria. When ammonia is created by the fish the bacteria eat it and begin to muliply. This takes a while. During this time there will be an excess of ammonia and nitrite. When the bacteria culture is mature, it will completely eat all of the fish waste. At that point the aquarium is declared ‘cycled’.

4. Fish in cycling

Easiest way to cycle your aquarium is by having a few hardy fish in the aquarium while the bacteria colony in the filter is maturing. The fish do suffer stress during this process which is why many advanced aquarists have turned to fishless cycling.
Recommended fish for a tropical aquarium are zebra danios, barbs, platys, or some of the hardier tetras. For coldwater the common goldfish is a tough cookie. For a marine tank blennies, gobies and perhaps damsels are possible candidates. Even though these fish are quite tough don’t be surprised if you have some fish deaths on the way to getting your filter matured.

You will need to do large daily water changes keeping the ammonia under 0.25ppm and the nitrites under 0.5ppm

A way to by-pass or reduce the risk of fish deaths during cycling is by priming the filter by squeezing the sponge from a mature filter into your new aquarium. The cloudy bacteria laden water will be filtered allowing the filter to have an instant colony of beneficial bacteria. You could also cut the sponge from an established tank in half and placing that in the new tank’s filter. You must also cut the new tank’s sponge in half and put that in the old tank’s filter.

Ideally you should have a low stocking level of fish. You will need to monitor your ammonia and nitrite levels daily. When the ammonia and nitrites levels start to drop off then you should be safe to add a fish or two. Then carry on the water changes and water tests. And when the levels drop off again then add one or two fish again. Repeat this process until the aquarium is cycled and the tank is stocked to your satisfaction.

5. Fishless cycling

This is the best way to cycle your aquarium but few aquarists bother with the extra wait before buying fish and with the hassle of buying ammonia and dosing their aquarium with ammonia every day.

Fishless cycling is a safe way to mature an aquarium without risking any fish deaths. And once the tank is fully cycled you can fully stock the aquarium.

Fishless cycling is also faster the fish in cycling because you can increase the amount of ammonia present in the aquarium which will encourage the beneficial bacteria to grow much faster. You can also have the water temperature higher in the mid 80s Fahrenheit. The higher temperature speeds up the life-cycle of the bacteria giving you a full colony of bacteria much quicker. The ideal level of ammonia is about 4ppm in a fishless tank. Higher levels of ammonia much above 4ppm will actually kill off the bacteria in the filter.

How to do fishless cycling

To do fishless cycling you will need to buy a bottle of pure ammonia without any scents or other additives. You will also need to buy an ammonia, nitrate and nitrite test kit. A few drops of ammonia need to be added every day with the aim of getting the ammonia level to 4ppm by using the test kit. If the reading is too high then reduce the dose and if the reading is too low then increase the amount. Always test after you add the ammonia. If the ammonia level is very high then do a water change to get the level down to close to 4ppm.

As with fish in cycling you can also speed up the process by adding bacteria from a mature filter. You can also add plants to help the process. You will have to do the occasional water change to keep the nitrate levels below 40ppm. And you will have to do a final water change to get the nitrate levels below 20ppm when you add all your fish.

When the bacteria is eliminating the ammonia and nitrite very quickly after you dose your tank with ammonia then you know your tank is mature and ready to cope with fish.

6. Recognising ammonia poisoning

If your fish are gasping at the surface or lethargic or have red blotches or have ragged fins or have laboured breathing or they are not moving much then it is likely they are suffering form ammonia poisoning. This usually happens several days after a tank is newly set up. At first the new tank will be fine but as the fish continue to poop and urinate in their own water, the ammonia from their waste is building up. The fish can cope with small amounts of waste but as it builds up it becomes lethal.

You must take immediate action to save your fish. You need to stop feeding your fish. You need to change 50% of the water with water of the same temperature and with the chlorine removed using a dechlorinator. Then you will need to test the water again. You need to get the ammonia level below .25ppm and the nitrite level below .5ppm. You should also consider spreading out your fish by putting some of them into other aquariums.

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