Aquarium Substrate

Choosing A Substrate For Your Aquarium

Choosing the correct substrate is one of the most important decisions you will make when setting up your aquarium. What type of tank would you like, for example, fresh water or marine? Are you only going to use artificial plants or would you prefer a natural substrate that enables you to grow live plants? Would you like your fish to breed?

Your substrate provides a home to the beneficial bacteria that keep your tank healthy and stable. It is important to make a well informed choice so that your tank is well balanced. Then you can spend less time maintaining and more time enjoying your hobby.

For the tropical or cold water fish tank

Smooth, natural gravel is one of the most popular substrates for these tanks. It is familiar to most fish and allows them to exhibit more natural behaviour and colours. Larger grades (6 to 10mm) are great for goldfish as they naturally feed from the bottom of the tank and smaller substrates risk being swallowed. Larger gravel also allows water to flow through it more easily and this provides oxygen to beneficial bacteria. Fine gravel or sand (1 to 4mm) is commonly used in tropical tanks or those with smaller fish where ingestion won’t be an issue. Plants can root better into fine gravel too and any waste or leftover food tends to be more visible and therefore easier to remove. Many aquarists use either a medium gravel (4 to 6mm) or a mixture of grades to share some of the benefits and create a more diverse aquascape.

Coloured gravel and sand

Gravel is available in a variety of colours. This is great if you have a theme for your aquarium or if you are using colours to compliment other furniture in the room. All of what has been said about the different sizes of substrate applies just the same. It is worth noting that Many people keep tropical fish because of their beautiful colours. Most fish have evolved these colours as a way of communicating with each other, either readiness to breed, social status, or to confuse predators. Bright substrates can confuse fish and as a result, many will mute their colour or pattern and appear relatively dull when very bright gravel is used.

If you are using internal or external power filters, you should have a gravel depth of around 1 to 1 and a half inches. If you are using an under gravel filter system, you will need approximately 3 inches of gravel.

For the planted tank

By far most aquarium plants acquire nutrients through their roots so it is best to have two different layers of substrate. The bottom layer should consist of a special planting substrate capable of holding on to nutrients. These should be porous to allow plants to anchor themselves down. This layer needs to be 1 to 2 inches thick for most plants to thrive. The top layer should be medium or fine standard aquarium gravel of 1 to 2 inch depth. This is because many planting substrates are quite sharp and could cause damage to bottom feeding fish such as corydoras catfish. Having the top layer of gravel prevents the nutrients in the lower layer from simply washing away and slows down the passage of water around the plants roots, enabling them to root firmly.

For the marine aquarium

When choosing the substrate for your marine aquarium it is important to remember that salt water fish and invertebrates require a high pH of around 7.8 to 8.4. This is the reason that the majority of salt water tanks use calcium carbonate based substrates. As the pH of your water naturally drops over time, these substrates will act as a natural buffer by releasing calcium into the water.

It is important to have an idea of the species you would like to stock. Many marine fish either pick up mouthfuls and sieve it through their gills or burrow into it. These species require a fine sand to do this. Larger predatory fish often swim mid water and so you can use a larger gravel or crushed shells . This can create a dramatic effect on the bottom of the tank. The species you decide to keep should determine what size gravel or sand you use.

If you want to keep a tank of mixed fish and invertebrates, you may want to have areas of the tank with different types of substrates. This can be harder to maintain but it is very rewarding to see many different creatures in their chosen element. It is important to research any animal before you buy and ensure you can provide it with everything it needs.

Other things to consider

Gravel is heavy! For every square foot at 1 inch deep you will require 4 to 5 kgs of substrate. Deeper substrate than normal is advised if you use rocks or heavy decorations in your tank. They will need to be placed securely so that they don’t move and harm your fish or damage your tank.

Always read the instructions when you purchase substrate. Some require washing before they are added and others, such as many planting substrates, do not. Doing so would wash away vital minerals. When washing your substrate it is much easier to do small amounts rather than all at once. The best way to do this is by pouring a few kgs into a bucket, adding tap water. Stir up the substrate before allowing it to settle for a few seconds and then pouring off the water. Repeat this as many times as is necessary until the water runs clear.

If you have a plastic or acrylic aquarium, you need to take extra care when adding sand or gravel as these tanks will scratch more easily than glass.

After adding substrate to an empty aquarium, place a saucer on top of the substrate. Then fill the aquarium by pouring water onto the saucer. This will ensure minimal disturbance and when combined with well washed gravel, will reduce the chance of cloudy water.

Most of all, have fun! Choosing the correct substrate will have long lasting effects in your aquarium. It will make maintenance easier and your pets happier. As long as your choice is well informed, the rewards are long lasting.

Download this guide as a PDF here Choosing a substrate for your aquarium

Tropical Freshwater Aquarium

How to set up a tropical planted aquarium

New to fishkeeping? This planted aquarium is easy to set up, and is suitable for beginners who would like to grow live plants in their community tank.

For our set-up, the aquarium we chose was a Juwel Trigon 190 with dark wood cabinet. The tank is a bow front corner aquarium which, due to its shape, should be placed in the corner of the room.

We chose the Juwel tank as it can accommodate a number of different fish types and it comes with a built-in internal filter and heater. The built-in filter makes equipment choice less difficult and this particular filter (minus the carbon pad) we found to be good for planted aquaria.

The heater thermostat, which keeps the water at the right temperature for the fish, sits inside the filter and is fitted in a place where it will receive a good flow of water. The heater is set to 25°C/77°F.

We built the cabinet ourselves as it came flat packed, so make sure that you assemble it correctly as the tank will be heavy once filled. Our tank can be viewed from both sofas in the room it’s in and is in the opposite corner to the television, so the two won’t clash. The corner is particularly suitable as there aren’t any radiators nearby which might cause the temperature of the tank to fluctuate. The French windows are opposite the tank but it is still the most suitable corner, and if sunlight does hit the tank during daylight hours, we can simply pull one of the curtains across.

Set-up type

The brief was to set up a tropical community tank with plants. A community aquarium is the most popular type of set-up – it houses a mix of fish that are all of a peaceful nature and a similar size, and which will all live happily alongside one another.

We wanted to add some real plants which make the aquarium look much more natural and also make the fish feel more ‘at home’. You can just add basic gravel, but if you want your plants to grow really well, rather than just survive, you really need to add a few extras to the basic set up. We started at the bottom:

One useful tool for growing plants is the undergravel heating cable. This low wattage cable (usually below 50W depending on size,) emits warmth which causes convection currents to move water very slowly through the gravel and with it, nutrients that can then be taken up by the plant roots. Heating cables don’t come with thermostats as they are generally not powerful enough to overheat the tank.

Not everyone uses heating cables but most successful planted aquariums do, and to fit one and then turn it off in the future is far less trouble than to not fit one and have to strip the tank in order to put one in.

Substrate is the aquatic world’s term for the gravel or sand that goes on the bottom of the tank. In this case plant growth was a factor and so we needed something to feed the plants, and something to anchor the plants. The fertiliser came in the form of Tetra Complete Substrate, which contains nutrients to aid plant growth. The ‘anchor’ was a 10cm/4” layer of Unipac Senegal grit. You need a deep layer so that the plants can send the roots down, and the grain size should be quite small to aid anchoring and to allow the roots to push their way through it.

Most substrates need to be rinsed in tap water to remove any dust which would cloud the tank water once filled.

Note that plant fertiliser substrates like the Tetra Complete Substrate should not be washed as all the nutrients and particles would be washed away – so only wash the sand or gravel that goes on top of the plant substrate.


Aquascaping is the term used to describe underwater landscaping, and it is a chance to create your own unique underwater scene.

Aquascapes should not only look good but should be practical for maintenance and sympathetic to the needs of the fish. Most tropical fish like to be able to hide if they feel threatened, so a combination of rocks, wood and plants will provide shelter. The lava rock we used has been carved to create holes and has good architectural qualities. It is inert, meaning that it won’t leach anything into the water that could poison fish or alter water quality.

The wood used is also for aquatic use but it will still stain the water quite brown. Ordinarily the carbon in the filter would help to clear the water of tannins but it was removed to prevent it sucking up the plant food.

Only buy wood from aquatic shops as it will sink and is safe for use with fish. The rock goes in first, then the wood, then the plants.


Plants are a major design feature of this aquarium so we used species we knew would grow quickly and were easy to keep. Fast growing plant species suck up the nitrates and phosphates that cause algal growth, and the tall species provide a bit of shade beneath them as they stretch across the water surface. We obtained ours from a mail order plant company and ordered a selection for a 90cm/36” aquarium.

We didn’t use all the plants that were sent as we didn’t want it to be too heavily planted, and instead just picked those that suited our décor and caught our eye.

Finishing touches

Carbon dioxide (CO2) was used to aid plant growth along with liquid fertiliser to be added on a weekly basis and reflectors to increase the amount of light shining into the tank. It is a good idea to plug your lights into a timer so that there is a fixed amount of light per day. This offers a natural day/night cycle for the fish and plants and prevents the light from being left on too long – causing nuisance algae.

Tapwater was used for the set-up, in the hope that initial planting would remove the nitrate and phosphate. Three weeks on and the plant choice was proving successful as no algae had grown and water tests revealed that the tank was ready for its first fish.

Hardy fish were added initially – some Platies and Golden barbs – and again the water was tested following their introduction.

Download this guide as a PDF here How to set up a tropical planted aquarium