Tetra Marine Advice

Tetra Marine Advice

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Types of marine aquarium

Many people start with a fish-only aquarium, as these tend to be the easiest to care for. This is because the fish are less demanding than corals and other invertebrates. However, this means missing out on the beauty and diversity that other life can bring to a marine aquarium. For this reason, basic reef aquariums are becoming increasingly popular, and are easily achievable. These contain a broad range of animals, including fish, less-demanding corals, shrimp, hermit crabs, starfish, and so on.


Because marine fish and invertebrates (corals, shrimp etc) are used to a very stable environment, they are best suited to an aquarium of 120 litres or more. However, if you are prepared to do a little more work to keep it healthy, small (“nano”) marine aquariums are becoming increasingly popular. Your aquatics outlet can advise you further on the choice available.

To keep them happy and the water healthy, marine fish should be stocked at a lower density compared to freshwater fish. Stick to 10 – 30cm of fish per 100 litres for the best results. This refers to the final size of the fish, not the size they are when you buy them.

Make sure the aquarium you choose is suitable for salt water, as it is very corrosive. The easiest way to do this is to buy one that specifically states it is suitable, or that comes as a complete marine aquarium kit. If in doubt, ask your aquatics outlet.


Complete kits should come with all the equipment you need, however in case you choose to buy it separately, the following is what you need for a basic reef aquarium:

· External filter, e.g. TetraTec EX: An external filter provides plenty of room for biological media, where friendly bacteria break down toxic ammonia. It sieves solid waste from the water, and can also be used to house other types of filter media if required (e.g. for removing nutrients from the water).

· Protein skimmer: Unique to marine aquariums, a skimmer is essential for maintaining the water quality needed by marine fish and invertebrates. It relies on tiny air bubbles to remove organic material from the water, collecting it as a foam that can easily be disposed of.

· Water pumps: Reef aquariums need strong, turbulent water flow. The return from the filter and skimmer may not be sufficient for this, and so it is well worth installing some additional circulation pumps. This will keep the corals healthier, and help to control nuisance algae.

· Lighting: Most corals have beneficial algae growing in their bodies which provide them with nutrients. These algae, like all plants, need light to produce these nutrients. Therefore, lighting has to be very good on a marine aquarium, and you should ensure it is suitable for corals.

· Heater, e.g. TetraTec HT: A temperature of 25 – 27°C is required for marine aquariums, and this can be achieved using a heater with an in-built thermostat, such as the TetraTec HT heater.

Live rock

Live rock is unique to marine aquariums, and can be thought of as an extension of the filter system. The rock used is very porous with a large surface area, and provided there is good water movement, it acts as a filter, helping to keep the water clean.

Another benefit of live rock is that it contains planktonic forms of many different marine organisms. These then develop and emerge from the rock once it is in the aquarium, providing a source of great fascination. It’s important to buy well-conditioned and properly maintained live rock to benefit fully from this.

In most modern aquariums live rock is considered essential, and should be part of your set-up. In any case, it will help you to create a more realistic reef display.


To create the right environment, use an aragonite substrate for your aquarium. This provides a source of calcium and bicarbonate, which are essential for a healthy reef. Your aquatics outlet can advise you further on suitable substrates.


Creating the right conditions for your marine aquarium is essential, and for this you need a good quality marine salt. Tetra Marine SeaSalt contains all the essential elements needed by marine life, in the correct proportions to support healthy fish and corals.

For a reef aquarium, you need to replicate the salinity of the oceans, which averages 35ppt (parts per thousand). Salinity can be measured using ‘specific gravity’ – a term that relates to the density of the water. When you first fill the aquarium, you can mix the salt directly into it. Do this once the temperature is correct, and all the equipment is turned on and working. Add Tetra Marine SeaSalt slowly, ensuring it dissolves completely. As you go, measure the specific gravity using a TetraTec Hydrometer. Once the water has a specific gravity of approximately 1.026, this relates to a salinity of 35ppt. Not all hydrometers convert specific gravity to salinity in the same way, so if you are not using a TetraTec Hydrometer, ensure you read the instructions carefully. In future, when you add new water to the aquarium you will need to mix it up before using it.

In most cases, you will be advised to use ‘reverse osmosis’ (RO) water for your aquarium. This has been filtered to remove everything from it, and provides a good starting point for mixing up seawater. You can usually buy this from your aquatics outlet. In some cases though, tap water may be suitable. If so, you must use Tetra Marine AquaSafe to make it safe for your aquarium.

Stocking the aquarium

Having set the aquarium up with the right equipment and water, you can then speak to your aquatics outlet about stocking it. Normally you will add the live rock first and allow this time to mature. Then you can begin adding fish and invertebrates, according to their recommendations. Add Tetra Marine SafeStart to the water whenever you add fish, to promote the development of beneficial bacteria, thereby preventing water quality problems.

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