Reef Aquarium Maintenance - Lighting

 

Many reef aquarium enthusiasts are well aware and keep a rigorous schedule of doing weekly and even daily maintenance on their reef aquariums to keep the water quality in check. From daily dosing of calcium and ph stabilizer to keep the alkalinity, ph and calcium levels at a level for optimum coral growth, to weekly water changes to keep nitrates and nitrites in check and add trace elements.

We all know about keeping the mechanical filters cleaned to keep from depleting oxygen levels. But may people forget about the importance of maintaining the lighting on their reef aquariums. It is not something that is noticed by the human eye because the change in intensity and color happens at such a gradual pace. The gradual deterioration of the lighting can be evident in several ways in the reef aquarium. There seems to be something wrong. The corals are not opening fully like they used to and some may even start to regress. There is suddenly growth of unwanted algae with seemingly perfect water quality.

You would not think of waiting until ammonia and nitrates get out of hand to start doing water changes, so why wait until the lighting has deteriorated to change the bulbs. Many aquarium light fixtures have a glass or plexiglass cover that over time will build up a fine coating of dust reducing the amount of light reaching the corals. This cover should be cleaned on a monthly basis.

The manufacturers for metal halides recommend changing the bulbs every six months. Fluorescent bulbs such as VHO, power compacts, actinic, and T5s recommend replacement at 8 - 12 months. Many studies have concluded that metal halide bulbs can loose up to 50 percent of their original intensity and color temperature with in 1 year. In other words, a 14,000K HQI bulb after a year could have a color temperature of 7,000K.

This would explain the algae growth since plants tend to utilize more of the red spectrum, while the zooxanthellae found in the coral tissues thrive more on the blue part of the spectrum. In simple terms, the higher the color temperature, the higher the blue part of the spectrum is visible and the lower the color temperature, the higher the red part of the spectrum is visible. To simulate the lighting for the reef aquarium we need to understand the light that occurs naturally on the reef with sunlight. The ocean has a blue color because it is the blue part of the spectrum that penetrates the water the deepest and the red and yellow are filtered out.

New metal halide bulbs need to have the arc tube chemicals "burn-in" for approximately 100 hours before they reach their optimum color and light level. This is why new lamps can sometimes be unstable or vary in color. Many manufacturers "burn-in" their bulbs before they are sold. As the lamps age, chemical changes occur in the lamp causing shifts in the chromaticity of the lamps. Different lamp designs shift in different ways, and different lamps from the same group may shift in different amounts.

Generally, over the economic life lamps will shift 200K to 300K in color temperature. As a group of lamps ages together in a facility, the lamps will generally shift at the same rate causing very little color variation from lamp to lamp. However, if new replacement lamps are introduced into the group of lamps, color differences may be more noticeable, because the new lamps have not aged and shifted with the remainder of lamps. This is just one of the reasons why many users prefer to group relamp as opposed to spot relamping.

Although Fluorescent bulbs do not have a burn-in time and last longer they tend to build up a coating on the tube, reducing the intensity and color temperature.

While PAR might be an unfamiliar term in comparison to the more often seen Lumens or Lux, it is by far the most appropriate way for us to assess light in connection with the reef tank since it measures the light intensity of the spectrum that is utilized by the corals. Lumens and Lux are measurements of how bright a light source appears to the human eye and as such has little relevance in the reef aquarium.

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