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The Ultimate Guide to Setting up and Cycling your Fish Tank

The many benefits of keeping fish is widely known, including a reduction in stress and improving your mental health. This in addition to busy lifestyles means less time to walk dogs and the bigger likelihood of opting for more passively kept pets - fish! There’s a huge range in tank sizes and styles as well as a huge amount of potential tank inhabitants that come in all shapes, sizes and colours. With all this choice available, you’re sure to find something that suits you as you venture into the world of aquariums.





For this article, we’re not going to discuss potential fish - you can read more on them here (The 10 best beginner aquarium fish). As well, if you’re wanting something a little more on the unusual side for your tank, you can opt for invertebrates! You can read more on those here (The best invertebrates for freshwater aquariums).


Instead, we’re going to focus on how you should set up your fish tank, covering how to prepare the tank, install the equipment, how to cycle your tank and then acclimatise your new fish.


Unfortunately it’s really common for pet stores to either sell tanks and fish together at the same time, or to sell fish to owners that have only had a tank set up for a few days. These fish are destined for high stress and a slow descent into disease and then death, we’ll explain why. It’s very important to fully cycle your tank before you add fish to it so that you know the water quality will remain high.



Let’s start at the beginning.

Step one is to plan your tank. What fish do you want to keep? Then decide how many you can keep in your tank, or decide how many you want, then buy a tank that size or bigger. It’s best to have some buffer space in your tank. Just because you can fit 30 Neon Tetra in the tank doesn’t mean that you should, you could mix and match.


Do you want to house a single fish, such as a Betta? Or would you like a couple of the same type of fish? Or you could even set up a few groups of small fish to build a community tank. The type of fish and/or invertebrates you keep will determine the size of the tank you need (hint, it’s always much larger than you’d initially think). It also tells you the equipment you’ll need, the water conditions you’ll have to maintain and potentially the type of plants you should keep, if you’re opting for live plants. For example, gold fish will eat most live plants.


Sit down and make a plan of the fish you like, research whether they’re compatible and then plan out what the best water conditions will be (pH levels and hard or soft water), decide whether you can have live plants, and then choose compatible plants (Java Fern is a great option for new tank owners - they grow easily and they don’t taste very nice so most fish wont eat them). You can also choose decorations at this point as well as the equipment.


For filters, you can either go with an Under Gravel Filter if your tank is small (under 50L), or a sponge filter. If your tank is larger you can go for a submersible filter, a hang on the back filter or a canister filter. For heaters, you can often find ones that will match your tank capacity. These will be fine, and it often takes up to 48 hours to get your tank water up to a set temperature.



After you’ve purchased all of your equipment then it’s time to prepare your tank! Before you start adding water you need to fully clean the tank to make sure there’s no dust or chemicals on the inside, as this can disrupt water quality over time. If you’ve got a new tank, just use a damp cloth and you should be able to remove all dust. Never use any soap or chemicals to clean anything that’s going inside your tank.


If you’ve got a second hand tank you can use vinegar and kitchen roll to clean the inside of the tank. Always opt for buying decorations from new, and clean those too. If your tank is acrylic then you may need softer cloth to clean so that you avoid scratching the tank.


After you’ve cleaned your second hand tank you need to assess it for potential leaks. To do this, just fill it with water up to a few inches and leave it for an hour. Afterwards, run your finger around each of the edges and see if you can spot any water. If you do, empty the tank and wait for it to dry, you can then use a basic aquarium sealant to reseal the tank. Simply squeeze some sealant out into the corner inside the tank, getting it as far into the edge as possible, then while wearing gloves, run your finger up the inside of the edge to smooth it over and wait for the sealant to cure. You can find aquarium sealant here.


Now that your tank is clean and sealed, it’s time to position the tank where you want it to stay. It’s important to do this now before you put anything in because it’ll get incredibly heavy once you start adding water. 5 inches in a tank doesn’t look like much but it could easily be 15 liters, it’s just easier to place while it’s light.


To find a suitable place for setting up your tank you’ll need to find somewhere out of direct sunlight, as this could cause algae to bloom very easily. You’ll also need a plug socket nearby too, preferably behind/under where the tank will be. Make sure that any stand you put the tank on will definitely hold the tank at full weight. For example, a 50 gallon tank typically weighs around 100lbs while empty. Once it’s full of water this goes up to 600lbs. Make sure you’ve got a base that can definitely hold that weight, as if it breaks you’ve got a pretty significant mess to clean up and a high chance of flood damage.


Once your tank is in position, make sure it’s level. You can do this with a spirit level if you have one, or you can fill it with a couple of inches of water and check by eye that it’s level. From the front, it should look equal on both the left and the right, however it’s also important to check that the front is also level with the back.





Once you’re in position it’s time to add your substrate. If you’ve opted for an undergravel filter, this is now the time to add it. If you’ve gone with this option then there’ll be a flat base with one corner that a tube connects to. It doesn’t really matter from a technical point where you place this tube - in one of the back corners is usually where you’d place them, however we’ve seen tanks where the owner has two UG filters placed in the center at the back of the tank facing away from each other, and this was a nice aesthetic.


If you’ve got plants and have opted for fertilizer for them, place this down first and get it into position. For example if you’re having your plants all on one side of the tank then you can have the fertilizer only on that side as the other side won't be used. You can also build up a sense of depth by raising the substrate towards the back of the tank. After this you can add the aquarium substrate.


If you’re opting just for a substrate of stones then you can also build it up towards the back to give a sense of depth to the tank too.


An important note on substrate is that sometimes your fish need certain types of substrate, for example some catfish need sandy substrates, fish that are prone to breeding will need smaller substrates so they don’t get any eggs trapped under it. If you’re adding plants then larger substrates will help the roots move through it and to the fertiliser.


When working out how much you need, a good rule of thumb is a pound of substrate per gallon of water, or 100g per litre of water in your tank capacity. This should ensure around about a 1” thick bed. If you want to raise up parts of the substrate, you should double this estimate.


You can use these figures as a guideline:

10 Gallon 10-20lbs

20 Gallon 20-40lbs

40 Gallon 40-80lbs

50 Gallon 50-100lbs

75 Gallon 75-150lbs

90 Gallon 90-180lbs

125 Gallon 125-250lbs

150 Gallon 150-300lbs


Remember different substrates weigh different amounts so the weight you’ll need varies. Smaller substrates often weigh more as they take up less space. Although your new substrate will come “prewashed” it’s a good idea to rinse your substrate before adding it to remove any dust from the factory or manufacturing plant. This will help you avoid dusty water once your tank is set up. To rinse out your substrate, put small amounts of it into a bucket and fill the bucket with cold water. You can use your hand to gently swirl around and through the substrate, empty the water and refill. Rinse and repeat til the water runs clear. This can take up quite a bit of time if you have a larger tank but it’s a really beneficial step.


If you have lots of gravel to get through, you could buy a larger bucket as it’ll also help during water changes, then keep the bucket under a running tap and swirl as it rinses. Keep doing this til the water is clear.


Some substrates like powder coated gravel don't do well by being washed like this, simply try to gently rinse them instead. Fertiliser does not need to be rinsed. Now your substrate is clean you can add it to the tank.

Start adding your substrate a small amount at a time until you’ve covered the base of your tank, then you can pour the rest over. Putting a thin layer in first will avoid scratching the base of the tank. While you’re pouring, think about where you want any raised areas. Usually the lowest point of the gravel will be at the front of the tank. The minimum depth of gravel should be one inch - your raised parts should be higher than this.





Now your substrate is in, you need to fill the tank up with water. If you’re using a tank on the small side, less than 20 gallons, then you should skip ahead slightly here and add your equipment first, then add your water. For everyone else though, let’s get that water in.


There’s two different methods here depending on if you’re having saltwater or freshwater fish. For freshwater, to stop the gravel being disturbed as you pour water in you can add a saucer or a bowl on top of the gravel and pour your water in to that. You’d usually place this in a space that’s easy to get to with the water - typically the middle. When the tank is full, now is the time to add your dechlorinator to improve the water quality. For dechlorinator, we suggest using Tetra’s Aquasafe - Tetra’s one of the biggest names in aquarium products and Aquasafe is one of the only water conditioners we at Your Pet Guides use in our tanks. The instructions on the back of the bottle will help you work out how much to put in your tank - it’s typically 5ml per 10L of water.


If you’re building a saltwater set up then you’ll need to prepare the water first. The water you use should have gone through Reverse Osmosis first, you can either buy RO water or you can buy treatments to add to the water. Typically you’d prepare the water in large buckets first. Also add a dechlorinator to the water too, again, we suggest Tetra’s Aquasafe for this. To turn this into saltwater, you can buy salt mixes that you just add to the water. Follow the instructions on the packet to make sure you add the right amount. Then you can add all the water to the tank.




Now it’s time for your equipment. At a bare minimum, 99% of set ups require at least a filter. Installations of filters depend on your brand and whether you’ve opted for an internal or external filter.


If you’ve got a sponge filter, assemble the parts together and attach your air pump hose to the filter. You’ll have suction cups at the back of the filter - use these to stick the filter to the back of the tank. If you want to add more aeration to the tank you can position it so that the head of the filter is above the water slightly so that it agitates the surface of the water. You’re probably fine with aeration though, as you’ll be using an air pump to operate the filter.


For an internal/submersed filter, assemble it before you add it to the tank, then stick it to the back wall of your aquarium with the top of the pump out of the water by a few centimetres. You can either have the outlet above the water if it’s supported by your specific pump to add aeration if you don’t have an air pump, or below the water line to keep the noise level down.


If you’ve gone for a hang on the back style filter or a canister filter you’ll have specific instructions from your brand to set it up properly - just follow these. External filters are usually better at filtering water as they typically have more space for filter media. Make sure your filter is fully set up before you switch it on - the water often acts as a lubricant and coolant for the pump and running it dry may damage it.


External filters usually sit within the stand, below the tank. An external filter carries the water out of the tank, and to the filter below to clean in, and then sends it back to the tank. Always make sure that the inlet and outlet tubes are straight with no bends or kinks so the water can travel out of (and back) into the tank freely.


Most external filters need to be full of water before you plug them into the power supply – this is called priming the system, which gets water moving through the filter.


After the filter comes the heater. A lot of the time in freshwater tanks you don't need a heater, however if you’re in a country prone to cold weather then this may be necessary for you to maintain a constant temperature of the time. Most heaters have a dial on the top to select the temperature you want, as well as a line on them to show how deep the heater should go into the water.


Always place your heater at one side of your tank, and a thermometer at the other side of the tank to make sure your tank is heated consistently. If you’ve bought any other equipment which needs installing, such as air pumps and stones or any lights, you should do this now. If you’re setting up a saltwater aquarium you’ll also need to install your protein skimmer and any other equipment you’ve purchased for your tank.




Now it’s time to add your plants and your decorations. It’s time to create the appearance you envisaged. It might be your choice to create a heavily planted tank, you could also opt for a very natural looking tank with natural stone, some plants and moss and maybe some driftwood. Equally, you might opt for a sunken pirate wreck and some fake plants. It’s all up to you! The last option is probably the easiest to maintain.


Whatever you do, make sure you rinse each of your decorations before you place them in appropriate places. When you’re positioning your plants you’ll see that some plants look better at the front of the tank, whereas some look better at the back. These are classed as foreground and background plants - typically larger or denser plants are more suited to the background, whereas thinner plants and types of moss and more suited to the front of your tank. When it comes to planting them, you’ll also need to make sure you follow the advice for each species. Most plants can be buried straight into the substrate, however some plants such as Java Fern and mosses need to be attached to driftwood before putting them in the tank.





One of the last steps, but one of the most important steps, is cycling your tank. Most of the time when you talk to employees at a pet store they’ll recommend you have your tank run for 24 hours before you add your fish - this is absolutely not advisable. Your tank needs to be fully cycled before you add fish, and this can take weeks or months. By cycling the tank we mean you need to let your tank build up beneficial bacteria so that the tank can go through a nitrogen cycle. This beneficial bacteria builds up in your filter and in your substrate and helps ammonia (a substitute for fish waste, harmful for your fish) break down into nitrite, which is also harmful to your fish, the bacteria then convert the nitrites into nitrates which are only harmful in high amounts.


To take measurements of the levels in your tank, you need to use a water test kit. We recommend using API's 5 in 1 test strips if you're new to Fish Tanks, or their Master Kit if you're okay with having a more scientific approach. The test strips are the quick and easy way to test the 5 most important aquarium water parameters – pH, KH, GH, nitrate, and nitrite – in one easy step. Simply dip one test strip directly into the aquarium, and compare the colors on the strip to the color card provided to help prevent invisible water problems that can be harmful to fish. Each kit includes detailed information on how to interpret the test results and correct unsafe water conditions.


The Master Test Kit measures the 4 most important levels in freshwater aquariums quickly and accurately, including pH, high range pH, ammonia, nitrite, and nitrate. With scientific accuracy for professional results, the reusable FRESHWATER MASTER TEST KIT comes with 4 glass test tubes with snap-tight caps and a convenient holding tub for easy storage. Also includes a step-by-step instruction booklet with a color chart that provides information on how to correct unsafe water conditions.


You can buy the test strips here.

Or you can go for the Master Test Kit here.


It takes time to build up the first set of bacteria that break down the ammonia, then colonies start developing which break down the nitrites into nitrates, which also takes time. After this process has occurred though and your nitrite levels turn to 0ppm, you know you’re ready to start adding your fish and that you have enough beneficial bacteria in there to tackle your fish waste. To build up more of these bacteria colonies you simply add more ammonia for them to consume. Having more of the bacteria means that waste can turn to nitrates quicker.


If your level of nitrates start to spike, just conduct a partial water change of around 10 to 20 percent, and keep the cycle progressing. Live plants also help to cycle through nitrites too, as well as removing CO2 and adding oxygen to the tank. In the beginning you may have to add your own CO2 to the tank unless you’re using an air pump.


We always recommend cycling the tank without any fish, so that they aren’t exposed to any toxins in the water.


To begin the cycle process for Freshwater tanks, add some ammonia to your tank. Depending on which you buy, the instructions will say whether to add a big dose at the start, or smaller doses daily. You can buy some ammonia here (it’s generally fairly cheap). The ammonia acts as the substitute to what will become your fish’s waste. Carry out water tests on your tank each week to check it’s levels. You’ll see high levels of ammonia, which will then convert into high levels of nitrites, which will then drop off as it becomes nitrate. Once ammonia and nitrite levels drop off to 0ppm, you’re all set for your fish to join the tank.


There are a few ways you can speed this up, the best is to add a filter from an established tank so your bacteria colony just has to reproduce, which it will do a lot quicker than starting from scratch. Another step to speed it up is to increase the water temperature which causes the bacteria to reproduce quicker. Also by adding oxygen to the tank with an air pump you can further speed this process up.



For a saltwater set up, the most common way to cycle your tank is by using live rocks. Whilst the rock isn’t actually alive, it is referred to as live rock, because this is where the bacteria build up. Always choose rocks which are light – this means it will have plenty of tiny nooks and crannies for the bacteria to build up, or a bigger surface area. Always transfer the rock from wherever you’ve bought it to your tank as quickly as possible to prevent the bacteria dying off. This will usually be done by keeping your live rock in a bag of tank water, which you then remove from the bag and quickly place in your tank.


You might find that the dead bacteria is enough to kick start the cycling process, but if not, you can follow the same step as in the freshwater step above and use liquid ammonia to start the cycle off.


This whole process takes around 6-8 weeks typically, you can do it quicker by following the speeding up techniques mentioned above. Once you’ve checked your ammonia and nitrite levels are at 0ppm, perform a 50% water change to remove any build of nitrates. Your nice bacteria are stored in your substrate and your filter, so water changes should be fine providing you aren’t doing a total clean up.


Congrats! You are now ready to add your fish!


Now it’s time to acclimate your fish to your tank. You’ve invested a lot of time and effort in setting up and cycling your tank and it’s finally time to get some tank inhabitants in there! If you’ve opted for more than 5 or 6 small fish, you’ll have to add them over a period of a few weeks or months, to ensure that your bacteria stores can handle the full force of your fish poop.


Fish are sensitive to any changes in their water be that the temperature or the quality. The purpose of acclimation is to ease them into a new environment. You can do this by:

  • Turn off the aquarium lights and the lights in the room.

  • Float the bag for 15 minutes to allow it to adjust to the temperature.

  • Cut the bag open at the top, and roll the bag down creating an air pocket so the bag floats.

  • Add ½ a cup of water from your aquarium to the bag.

  • Repeat every 4-5 minutes until the bag is full.

  • Discard half of the water from the bag (not into the aquarium) and add ½ a cup of water again, every 4-5 minutes until the bag is full for a second time.

  • Using a net, slowly pick up the fish and remove it from the bag, adding it to your aquarium.

  • Discard the water in the bag.

  • Observe your new fish over the next 24 hours period to ensure they are settling in well, and eating properly.


Your tank is now all set up! Hopefully with this guide you’ll feel at ease setting up your tank. It’s a lot of information all at once but when you spend the time doing everything, you’ll be taking it all bit by bit, so don’t worry!


After your tank is set up, make sure you’re only doing water changes of around 10-30% unless there’s something wrong with your water conditions that are threatening the life of your fish. When you clean your filter or your decorations, gently wash them as you do a water change so that you can use the discarded water. If your filter has a sponge, just submerse it in the water and squeeze it gently till the waste is off it. Never rinse either your filter or your gravel in freshwater as this destroys your good bacteria colony, resulting in your tank cycling again. This process is a lot more dangerous to do when there are already fish in your tank.


Thanks for checking out this Fish Article! Here's a list of our other popular articles:

How To Set Up Your First Aquarium

Common Care Mistakes in First Time Fish Owners

The Beginner's Guide to Planted Tanks

The Minimal Maintenance Aquarium Set Up Guide

How To Clean Your Aquarium and Decorations

How To Spot Illnesses in Fish

Clean Up Crews for your Freshwater Aquarium

The Best Algae Eaters for Freshwater Tanks

The Best Aquarium Invertebrates



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