Another important topic – all life requires light, be it plants for photosynthesis, the creatures that rely directly on those plants or those further up the food chain.
This remains true in the aquarium (except perhaps for the most sterile ‘fish only’ system). Plants need both nutrition and light – you supply the first by feeding your fish and the subsequent waste generated (remember the nitrate cycle?), but lighting needs to cater for specific needs. It needs to be of high enough intensity, and of the right ‘temperature’ (degrees Kelvin) to enable photosynthesis. The wrong levels encourage the growth of nuisance algae which can smother and kill other plants.
In a reef environment, correct lighting is even more vital, not only for plants (as with freshwater), but for corals – many of these rely on a symbiotic relationship with algae within their tissue (zooxanthellae) for nutrition. Indeed, it is these corals which generally prove to be most successful in aquariums – we merely need to provide the right lighting though food is also taken from the water column. Corals that are not light dependant are often much harder to maintain as we don’t yet know their requirements. This may be a slight generalization as there are always exceptions – there are some excellent books for reference.
Daylight has a ‘temperature’ of approx. 5600 degrees Kelvin so ideally lighting should be in this range. Lower ‘temperatures’ can stimulate the growth of nuisance
algae or bacteria (e.g. Cyanobacteria which can be a nightmare to get rid of!), though excess nutrients are the main factor. These lower ‘temperatures’ create light in the yellow or red spectrum and thus give an aesthetically displeasing look in the aquarium. Daylight bulbs are now made specifically to cater for this at various temperatures (5700K,6500K,7500K etc) which produce a nice white light.
Things are slightly more complicated in the reef aquarium, in that as light penetrates water the reds & yellows are absorbed with only the blue wavelengths reaching very far down. Lights are manufactured to cater for this and the aesthetically pleasing look of bluer light (10,000K,14000K and even 20,000K).
Light is measured in a number of different ways – the one we know best being in Watts. Intensity is an issue in all aquariums (plants need enough to grow, but many of the fish we keep live naturally in sheltered environments so it should not be too bright).
Again, intensity is of greater importance in the reef environment as some corals and invertebrates require large amounts of light in order to survive. A general rule of thumb has been suggested of between 3 and 5 watts per gallon. Unfortunately, this is not a very useful suggestion as tank dimensions differ – 150W should be enough to penetrate 12”-24” deep tanks sufficiently. Many tanks are 24” or more so consideration needs to be given to that – 250W or more. Also there needs to be sufficient light to span the length of the tank.
As discussed above, lighting is very important and normal Tungsten bulbs give out the wrong spectrum. Halogen too is not really what is required though itd is used on some small ‘all in one’ tanks.
This is where specialist lighting comes into play:
these tubes are produced in lengths to fit most tanks and in a wide variety of colour ‘temperatures’ to suit most needs. There are the older style ‘T8’ tubes and now the ‘T5’ tubes – these were supposed to be as good as metal halides, but have not yet replaced them. T8 and T5 refers to the tube diameter (in 1/8ths of an inch) – the T5s are supposed to be more efficient due to their smaller diameter. This allows reflectors to send more of the light back past them and also gives more room in the aquarium hood for more lights.
these are another relatively new innovation and they give a crisp white light. Some believe they are not as efficient as the T5s due to their design limiting reflected light. However, one possible advantage is that their useful lifetime is better (maybe 18 months – see below).
these have been and are the mainstay of reef-keepers in particular – they produce large amounts of light a small source allowing them to penetrate deeper tanks. They give a good colour (usually 10,000K or 20000K, though a 14,000K version is produced as a good mid-point). These are often supplemented with one or two ‘actinic’ blue fluorescent tubes – this improves the aesthetic looks of the tank and causes many corals to fluoresce beautifully (this is what draws many people into reef-keeping).
Whichever type of lighting you decide upon, remember that a bulb’s output deteriorates over it’s lifetime – the change in spectrum could encourage the growth of nuisance algae or even affect corals adversely. As a rule of thumb, change the bulbs every 12 months.