Can Natural Aquarium Lighting Work?

The wild coral reefs sit under the sun and do well. Everything is correct – spectrum, intensity, photoperiod and the dawn/dusk sequence. Could the aquarist make use of Nature’s original?

For aquariums that contain corals the importance of aquarium lighting runs a close second to seawater quality, so it would seem reasonable to consider using the natural stuff. There are potential problems however.

The first consideration is sunlight and its availability. The skies over wild reefs are often blue but not always, clouds pass over and sometimes storms. Therefore continuous sunshine is not a necessity. However, for most of us in temperate areas the amount of cloud we experience is much more and I wonder how the zooxanthellae (algae within corals) will fare. They need the correct light to prosper and it is probable that the corals would have problems.

There are aquarists in blue sky areas where cloud cover is not so prevalent, and maybe the sunshine periods are not too far off those on wild reefs. So using natural light is more of a proposition. How could the sunshine be directed to the aquarium from the top? Allowing the sun to shine on the front glass of the aquarium could produce excessive algae growth there, thus spoiling the aquarist’s view and causing excessive cleaning of the glass. If the seawater is of high quality with little or no nitrate and phosphate, as it should be, algae growth within the aquarium shouldn’t be a problem, but it always surprises me that the stuff does appear quite clearly on viewing glasses nevertheless. Having said all that, if there is a fairly substantial nitrate and/or phosphate presence then algae could well proliferate much to the aquarist’s annoyance – the word sunlight could well turn into sunblight.

The answer could be to put the aquarium in a room below a low roof where a roof window of suitable proportions has been provided. This would allow the sunlight to slowly hit the top of the aquarium, reach full intensity, and then slowly reduce again. The risk of the seawater overheating would also be much reduced.

I am only aware of two aquarists that have used natural sunlight, and in both cases am not aware of the complete result.

In the first instance the aquarist did in fact have a window in the roof more or less as described and the corals did well for a while. Unfortunately, the area of the world where the aquarist lived meant that the sun dipped towards the horizon as the seasons changed and the sunlight became too weak or missed the aquarium completely. I feel sure the aquarist would have known the sun would do this but he must have miscalculated. What was done about it I don’t know – I’m sure putting the aquarium on wheels wasn’t an option!

In the second case the aquarium was located in a conservatory. There were too major problems, I know that one was fixed but don’t know about the other.

Clearly, in a conservatory with its glass roof and sides sunlight would have unrestricted access. Conservatories when bathed in sunlight can become very warm – this is one of the attractions of them. Unfortunately, this warmth caused problems with seawater temperature stability, usually climbing too high. The aquarist obtained a cooler (chiller) and as far as I am aware this cured the problem. The second problem was as mentioned earlier – algae. This algae not only caused very regular cleaning of the viewing glasses to be required, but caused excessive algae growth in the aquarium itself causing the aquarist to appeal for assistance (generally, not to me personally). I noted the nitrate level was quite high (if I remember correctly it was about 30ppm) but there wasn’t a mention of phosphate so that could have been anything. The aquarist was advised to reduce the nitrate level and reduce and control the sunlight (how?) but didn’t respond further. Perhaps the aquarium was re-located.

A keen advanced aquarist experimenting is great and this is how progress is achieved, and is to be applauded. However, with the hobby in the position it is today the usual path with lighting is better for most.

The aquarist can have lighting exactly suited to his/her needs relevant to the livestock being kept. That lighting can be closely controlled by the use of electric timers and an acceptable dawn/dusk sequence introduced, and the photoperiod adjusted according to need. For the great majority of us electric lighting is the answer.

  1. Very interesting, but I am not sure I like the idea about the aquarium in the conservatory, unless you can get natural cool air circulation in there, or alternatively use a cooler as you described it above. It is a probably a bit too risky for the fish. The old, “too cold in the winter, too warm in the summer” springs to mind. (I am a builder in London and although we have installed numerous conservatories over the years, we have never installed an aquarium in one.)

  2. Hello Martin.
    I wrote the text from an ‘interest’ point of view, personally I would not keep an aquarium in a conservatory. My own view is that the aquarist needs close control of the aquarium parameters and the sunlight would cause additional electricity hungry equipment to be required – more seawater heating for the winter and cooling for the summer. There’s also the consideration of too much algae…..

  3. Thank you for clearing that up. John.

    I am not an expert on aquariums, but it certainly did not sound right to me.

    Have a lovely weekend.


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