Refugium Lighting
How much light do I need?
Proper lighting is essential to a healthy, thriving refugium. Depending on the size of the refugium and what it will contain, there are many options to choose from. The best source for lighting refugiums would be natural sunlight but this is normally not an option unless setting up a planted tank. Most marine plants and algae require moderate to high light output, as they grow in fairly shallow environments in their native ecosystem. A few exceptions are many of the red algaes that are found growing in depths of 30 meters or more, and several species of caulerpa that prefer to grow under ledges and so require less intensity.
A good rule of thumb is to provide 3 to 4 watts per gallon for most plants and algae. Most manufactured refugiums however are very shallow so the intensity can be adjusted accordingly. Generally, full spectrum bulbs ranging from 6400K to 10,000K are appropriate. Some have had success with actinic bulbs in maintaining deep water algae, but these algae will grow regardless under standard full spectrum bulbs. Although using a 50/50 mix is more esthetically appealing and allows the addition of several varieties of soft corals if desired. Compact fluorescent bulbs are the least expensive and offer the most intensity for the money and are the preferred choice for illuminating refugiums.
Lighting Duration?
There is some controversy regarding how much light a refugium needs on a daily basis. In it's natural environment, depending on the season, plants and algae have sun for 12 to 14 hrs a day. In nature there are many factors that affect the intensity of this light, such as overcast skies, and coastal storms that cloud the water, etc. With most refugiums 10-12 hours of direct lighting is sufficient.
Reverse Cycle?
Reverse cycle
lighting simply means to illuminate the refugium while the main display tank
lights are off. There are several benefits to this type of lighting. During the
day plants and algae give off oxygen through photosynthesis, however when it is
dark, they use the stored carbohydrates just like animals and respire
carbon-dioxide, this can cause the Ph to acidify. The thought is that a balance
is achieved in having the main tank opposite the growing refugium inhabitants.
Another benefit is the reduced heat that would have been created by having the
systems run simultaneously.
24/7 Lighting?
Research has shown that caulerpa and some vascular plants can be illuminated continuously without ill affects to the fauna or flora. This method was introduced primarily to control sporulation in caulerpa species. Sporulation is the result of the reproductive cycle of marine algae, which dies and releases spores into the water to attach and grow to new areas. Sporulation is triggered by several things including a drastic drop in ph, temp, salinity or with an overall depletion of available nutrients. It can be avoided by keeping conditions stable and not introducing new algae to poor growing environments. This method of lighting does work and can be used to create more growth, in return exporting nutrients faster. The downside is the cost and heat associated with continuous lighting.