Softie Aquarium Lighting vs Reef Natural Sunlight

[philaquarist]

Hi folks,

There are some of us who still seem to have a difficult time accepting that we need very strong lighting for our softie tanks. Many folks (even here in RP) still preach the typical "2 to 3 watts / gallon" figure for softie tanks, which I guess is the most common "answer" you would get by Googling the Internet for it. Which proves my assertion that you simply cannot trust something because you were able to Google for it..... but that's OT.

To place things in the proper context, I am quoting some measurements of actual irradiance on a coral reef near the equator, done by J. van Ommen (originally published in a Dutch aquarium journal in 1992), but referenced by Fossa and Nilsen in their famous 1996 book "The Modern Coral Reef Aquarium".

During mid-day near the equator, irradiance in lux (or lumens per square meter) was measured as follows:
Ocean Surface >>> 114,543 126,520 77,420
5 meters deep >>> 28,636 31,630 19,355
10 meters deep >>> 16,039 17,713 10,839
20 meters deep >>> 9,136 10,122 6,194
The three numbers refer to 1) the minimum observed irradiance; 2) the maximum observed irradiance; and 3) average "real" irradiance, including cloud cover, etc)
<Pls note that almost all Cartimar corals are collected from between 1 to 3 meters depth).

Of course, the above measurements were done at the peak time (mid-day or 12noon). In 1989, Sauer published a graph of light intensity in a reef, measured over the whole day. Sauer showed that in a reef, the actual figures are about 80% of maximum at 10am and 2pm, and maybe 50% at 8am and 4pm. If you do the calculus for it, over a 12 hour photoperiod, the "real-world" light intensity would be around 50% of the average real irradiance figure (i.e., take the third number in the table above, and adjust downwards to 50% of the original number).

How do our aquarium lights compare with this? A typical 400w MH bulb generates about 35,000 lumens, while a typical 250w MH generates 19,000 lumens, and a 150w MH typically generates around 11,000 lumens. A typical 54w T5 HO bulb is rated for around 5,000 lumens, while a typical 39w T5 HO bulb is rated for 3,500 lumens, while the 24w T5 HO bulb is typically around 2,000 lumens. But don't let any of those theoretical figures deceive you! Why? Because there is severe (exponential?) degradation of lighting intensity as you go deeper in your tank. This is true for all bulbs, but is less for MH as compared to fluorescent bulbs (quite bad for T5 HO, very very bad for T12 NO).

Nilsen and Fossa made an experiment using 400w MH bulb in a live tank, with a distance of 15 inches from the bulb's center to the water surface. At source, the light had an irradiance of 35,000 lux. Then they measured actual light intensity at various depths of the tank. Directly under the bulb, but one inch below the water's surface, the figure was down to about 21,000 lux (or 60% of the lamp's theoretical lighting intensity). At 8 inches directly under the bulb, the figure was now only 14,000 lux (or only at 40% of theoretical light output). At 16 inches aquarium depth, the figure was only about 8,000 lux (or down to 20% of light output).

We also know that T5 HO irradiance weakens much more dramatically as you move deeper under water. I have not been able to get any similar scientific measurements for T5 HO, but we know that the the degradation is much worse than MH (at 16", the reading is almost zero lux, and that's assuming the bulb is just 3" directly above the water surface).

With the above information, consider a Sarcophyton colony living at a depth of say 2 meters (a very typical reef situation). If we interpret from the table above, this coral gets exposed to an average real irradiance of somewhere between 77,420 lux at ocean surface and 19,355 lux at 5 meters depth (using the third column in the table, assuming real-world conditions, such as clouds). Using very rough interpolation, let us say that the approximate figure for 2-meter depth is 50,000 lux. Since this is the peak noontime figure, let us take about 50% as an average real-world figure (from 6am to 6pm), or say, 25,000 lux.

To achieve approximately the same lighting intensity for the same coral placed 8" deep in the water of your tank, you would need to use a 400w MH bulb 15" directly above the specimen (which will effectively generate 21,000 lux at 8" of tank depth)!

How about using 54w T5 HO to achieve the same lighting intensity? We can compute at 5000 lumens per 54w T5 HO bulb at source. If we assume a worse degradation profile compared to MH (say, assume that at 8" depth, we will get only 30% of the actual figure at source, or effectively 1500 lux per bulb at 8" tank depth), then we will need about 16 bulbs of 54w T5 HO to get the same lighting as in nature. Actually, some scientist had done the calculation already, and came out with a figure of 38 bulbs of 54w T5 HO to achieve the same effect as real-world sunlight (with occasional clouds and all) that a coral gets when it lives close to the water surface. Which of course is impossible, as there is no way you could physically fit 38 T5 HO bulbs over one single coral specimen!

Thus, when I recommend that you should place 8x54 watts T5 HO on top of your 4 feet long softie tank, it is still a very far cry from mother nature's delivery of sunlight.

I wrote down this long-winded piece to stress my point: if you want to succeed in the reef aquarium hobby, you will need to invest in very good lighting. If you cannot afford to do this, then maybe you should just stick to FOWLR or FO.

Again, I post this in the spirit of sharing useful knowledge and information with other hobbyists.

Phil

OT: BTW, that is another advantage of tank-bred corals. Most of them have adjusted to aquarium conditions (meaning, they have gotten used to much less light than in natural reefs). They have adjusted in many ways, including increasing the quantity of their zooxanthellae (which explains why many aquacultured SPS are more colorful than those found in nature).

This also leads to another philosophical question: most tank-bred corals (not so much for softies, but more for SPS) are assuming new forms and new colors that are not found in nature! Are they still members of their original species, or have they effectively evolved into a new species? In fact, coral expert JEN Veron even asks the question: is there even such a thing as different "species" among corals of the same genus, or is the distinction meaningless?

[seriousreefer911]

[audioactive08]

[philaquarist]

I don't really understand serioureefer's question, nor its connection to my post

Anyway, for further clarification, every photosynthetic coral has three important light levels that govern the photosynthesis of its zooxanthellae:

1) there is a minimum level of light for the coral to survive. This level is called the "compensation point", where light is just enough to induce minimum photosynthesis. Below this, the coral will slowly die. In fact, most corals will not surrender: they will try to keep zooxanthellae, hoping the light will still increase. But after some time at this level, both the zooxanthellae and the coral will die.

2) there is a such a level called "photosaturation point". Generally, the more light, the more photosynthesis. But only while you have not yet reached the photosaturation point. Beyond the photosaturation point, even if you increase the light, there is no more added benefit to the coral.

3) lastly, there is a level called "photoinhibition point". This is the point where there is too much light, enough to damage the coral. At this level, photosynthesis will shut down. Most corals will expel their zooxanthellae (hoping they will be captured and will survive in another coral).

Obviously, for any coral to live, it must have light between 1) and 2). For any coral to optimally thrive, it must have light almost at or equal to 2). If the light is between 2) and 3), it is just wasted (no more incremental benefit to the coral) .

But corals are capable of "photoadaptation", where they adjust their behavior to adjust to the available light. Photoadaptation has its limits though, corals cannot go below level 1), nor go above level 3). BTW, this is most particularly noticeable in tank-bred corals, where their lighting needs may no longer be as much as their wild brethren.

For your Xenia, I have two comments:

a) Clearly, your tank lighting is still between levels 1) and 2), allowing growth and reproduction of the coral. With 4x24 watts over a 20 gallon tank, that is quite bright

2) But I am sure if the same Xenia corals were under direct sunlight, the growth would be even much higher.

I hope I answered your question, even if I did not understand your point

Phil

[seriousreefer911]

got it!tnx,sabagay 3x 32w ang t5 ko,1 24w,and 2x 20w na blue,hehe,

[gonzaimaki]

UP

again very informative article for newbies and softies tank.
Old post na pero very useful padin..