Choosing an aquarium light

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The most common question we tend to get asked regarding lighting is how much do you need? It all depends on what you are keeping in your aquarium. If you don't want to grow plants or you're just sticking to undemanding plants like Java fern or Anubias, you'll most probably be fine with one fluorescent tube.

However, if you want lots of plant growth or you want to grow more demanding plants, you'll need a minimum of two fluorescent tubes - maybe even five or six!

Similarly, if you're keeping only marine fish, one tube will be sufficient - but if you want to keep most inverts, you'll need at least four tubes.

Use a mixture of bulbs to get the best spectrum for photosynthesis and aesthetics.

There are several types of fluorescent tubes on the market, but T5s and T8s are the most commonly used. T5s are 5/8" diameter, while T8s are 1" in diameter.

High-output T5s have an output power in watts that is greater than a T8 of similar length. Two T5s give approximately the same output as three T8s. But the standard T5s don't differ that much to normal T8s in output, although they may have a longer lifespan if they run from an electronic ballast.

If your tank is deeper than about 60cm/24", you'll probably be better off with T5s or, better still, metal halides, which are more powerful and will penetrate deeper than standard T8 fluorescents.

Plants, corals and fish are adapted to a photoperiod of 12 hours of daylight followed by 12 hours of dark, so it's best to try and stick to this in your aquarium if you can. A plug-in timer is useful to turn the lights on and off.

The output of your lights will drop over time, and you may not be aware that this is happening. Make a note of the date the tubes were added and change them every 12 months or so, or when their output drops by a third (this can be measured with a lumen meter) - you'll be amazed at the difference adding new ones makes to your plants or invertebrates.

You can boost the amount of light that your plants and corals receive by adding a reflector to each of your lamps. Also ensure that any cover glasses stay clean.

There are a number of specialist tubes on the market aimed at plants and corals - or even just designed to help you get the best colours from your fish.

The "K" is the Kelvin rating of the bulb and shows the colour temperature. To oversimplify a little, sunlight has a Kelvin rating of about 6000K, so bulbs in this general area produce light that is similar to daylight. Kelvin numbers below 6000K look warmer and the light appears more orange or yellow. As Kelvin numbers get higher, the light looks cooler and has a more stark white or blue appearance.

An actinic bulb has a spectral output of 420nm. This is a very useful wavelength for corals that will help promote fluorescence. This bluer lighting replicates the effect of lighting at greater water depths. Progressively with depth, coloured light is filtered out until only blue wavelengths penetrate the water.

A fluorescent tube needs to be powered by a starter unit. These come in either magnetic forms or in newer, more sophisticated electronic forms.


Metal halide lighting
Metal halide lighting is much more intense than other types of lamp and can penetrate much deeper water, so it's ideal for light-loving plants and invertebrates, and also for taller aquaria.

It also provides a more natural type of lighting - you get shadows and glitter lines with metal halide lighting, which you don't get with fluorescent tubes. Some people use a combination of tubes and metal halides to get the lighting effect they want, or boost the actinic light for corals.

Metal halide lamps are either suspended from the ceiling or fixed to the wall (although you can now buy units that have their own stand), and are best used without cover glasses or condensation trays.

They are more expensive and can get quite hot, which can cause tanks to overheat, particularly in the summer. Follow the manufacturer's installation instructions as they need to be far enough away from the aquarium to avoid any splashes and to prevent overheating of the water.

You might also find you lose a lot of water in evaporation - an automatic top-up system isn't a bad idea. You will usually need one unit for each 45-60cm/18-24"? of tank length.

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Do you need a heater, and if you do, which type should you choose?

It's fair to say that the majority want a temperature of 24-26°C/75-79°F, and they also want that temperature to be stable. While many fish in temperate areas have adapted to temperature ranges from freezing up to 30°C/86°F, wide fluctuations in temperature aren't tolerated by most tropical fish. They could cause stress and lower the fishes' resistance to disease.

A heater-thermostat, or heaterstat, will provide fairly accurate, constant warmth for your tank, provided you pick the right size and allow for the room it sits in.



So how do they work?
As the name suggests, a heater-thermostat contains a heating element and a thermostat in one sealed unit. Despite the advent of microchip technology, the majority of heaters are still controlled by a bi-metallic strip thermostat.

These are usually brass on one side and steel on the other, which expand and contract at different rates when the temperature changes. When heated, the strip curves toward the steel side. When the water is cooler, the brass contracts and the circuit closes.

Electricity then passes through a contact on the end of the strip and the heating element warms up. A small magnet is often added on the underside of the strip to help close the connection. These strips respond to temperature changes with an accuracy of about +/- 0.25°C. But they do have a tendency to stick in the "on" position.


How reliable are they?
Although most aquarium equipment will last for years without problems, most fishkeepers will experience a heater failure at some point. The unfortunate problem with most heaters is that they tend to fail in the "on" position and can raise the temperature of the water to a dangerous level for the fish in a remarkably short space of time.

There's little you can do to prevent this, other than sticking to tried and tested brands with a good reputation for reliability, using just enough heating for your aquarium along with a reliable thermometer or electronic monitoring system.


What do I do when a heater sticks "on"?
Unplug it and leave it in the tank. If it's been stuck "on" for long, it's likely to be dangerously hot and will shatter if you cool it too fast.

Add extra aeration via any venturi on your filter or an air pump as the water will be extremely short of oxygen. Warm water holds less oxygen than cold.

This is one situation when it's hard to avoid stress if you’re to save any fish. A cool water change with dechlorinated water is your best hope – as much as 50% may be needed. Afterwards you’ll just have to monitor your fish with care – there's every chance that they will develop stress-related illnesses.


What heaters are available?
The standard is the submersible heaterstat. These can be fully submerged, which means that you pre-set the temperature, tuck them behind the decor, then plug the heater in. Never turn a heater on when it isn’t submerged. Try to leave any monitor light visible so you know that the unit is working. Monitor the temperature in the tank to ensure it is working.

Substrate heater: This is usually a cable system aimed at gentle heating, not warming the whole aquarium. It lies in a "snaky" curve under the substrate in a planted aquarium. The gentle heat causes nutrient-loaded water to rise gently, producing warm zones at the base of the tank. This heater is controlled by a thermostat and is usually supplemented with a heaterstat in the main aquarium that does the bulk of the work.

In-line heater: This relatively new variation is installed in-line in the return pipe from an external filter. It takes all the equipment out of the tank and is said to be very efficient.


What size do I need?
Most manufacturers produce a range of heaterstats designed to fit certain standard sizes or volumes of aquarium. On larger aquaria, it may be safer to fit two half-sized heaterstats as one overheating will not have such a devastating effect.


What temperature should I set the heater to?
This depends on the fish and occasionally on the effect you want to have on them. Certain species react to higher or lower temperatures by spawning, and others respond better to medications when the temperature is high. Some parasites are easier to kill when you use heat to speed up their life cycle. Equally, filter bacteria will multiply more quickly at the right temperature.

Some species, including some killifish and Discus, come from warmer tropical waters which have less or no flow, lower oxygen levels and higher temperatures. On the other hand, some species from mountain streams need slightly lower temperatures and higher oxygen levels. Some Corydoras species fit this bill.


Will an exposed heating element harm the fish?
There is the odd horror story about catfishes and other relatively sessile species burning themselves by lying against a heater. However, many modern systemised aquaria hide the heater safely inside the filter unit, usually in the outflow where it is especially efficient.
You can also buy heater guards to cover the heater to prevent this. These offer some protection should any decor collapse and smash the heater.


How can I protect myself?
Although we've not heard of anyone who has been killed by a heater, personally, i do have had quite painful electric shocks through mishandling heaters. Unplug them before handling them in any way.


Cold room?
If your aquarium is situated in a cold room, you might need more heating than normally recommended for your aquarium size. In an overly warm environment, the heater will rarely come on.