The aquarium looks good to you. There are some beautiful coral and there are some nice-looking green plants in it. But something seems off, maybe the colors aren’t vibrant. Maybe the algae is all over tank despite your best efforts to get rid of it. Chances are high that this isn’t a chemical water issue. In fact, it’s nearly always going to be a lighting issue.
Light is so much more then just an on-off switch for most of us hobbyists. A living underwater world depend on a far more complex frequency; one that we can understand if we know what spectrum to expect. It’s not all about how bright the light is but rather what part of visible light range it contains. Different wavelengths cause different biological reactions, as shown in infographic above. For example, red light get absorbed rapidly at surface and stimulates photosynthesis by stem plants. Meanwhile, blue light penetrates deeper into the water column and is responsible for powering symbiotic algae of deep-water corals.
Why Aquarium Lighting Matters
So if you have nothing but goldfish in a shallow dish, then forget about the spectrum, it really doesn’t matter. However, as soon as you introduce stony corals or demanding aquatic plant, each nanometer becomes currency. It’s not just a question of what you prefer to see in terms of pretty colors, but also matching light source with evolutionary history of organism.
So that leads me to the Kelvin rating, how warm or cool the output is. Cooler daylight ranges (sixty-five hundred Kelvin) is generally good for freshwater planted tanks because they mimic natural overhead sunlight and allow plants to absorb maximum amounts of chlorophyll. On the other hand, reef tanks frequently need far higher color temperatures approaching fourteen thousand or even twenty thousand Kelvin. That gets really high but it produces a stark blue hue that triggers fluorescent proteins in coral tissue. To our eyes, it may appear unnatural but that’s precisely what hard corals need to survive and reproduce. Warm white light will not do the trick on reef tank.
Most beginners fail because of intensity. Most people don’t understand that light quickly loses its energy as it moves into a body of water. Six feet above surface, a bright lamp produces almost nothing useful for photosynthesis. Half the photons are gone by twelve inches due to scattering and absorption. That’s why measuring at substrate level is non-negotiable. While low-tech plants can get by with minimal output, high-light species such as Acropora corals and red stem plants needs intense, direct light. You’re just guessing without an accurat measure… and guess what? Guessing typically results in rotting/bleaching plant material that feeds into the very algae outbreak you’re attempting to avoid.
Lighting schedule (photoperiod) is just as important. Twelve hours on and zero hours off may appear generous, but this often provides an opportunity for nuisance algae to get upper hand. Here is the solution. Many smart aquarists practice a midday siesta; i.e., turn lights off for a few hours in the middle of the day. This can decrease average light dose per day yet maintain high intensity at those times that the light is on. This lowers the CO2 demand and disrupts the unbroken period that algae use. Remember: consistency trumps length. An erratic 12 hour schedule isn’t always better than a consistent eight hour one, plants will adjust to the regularity and predict its pattern.
You will find that there are some trade-offs when selecting your lighting technology: heat, cost, and control. While LEDs dominate most of market now because they’re efficient and you can create custom color ranges, many reef keepers appreciate the natural shimmer from older metal halide bulbs (for aesthetics). Just be sure whatever you choose can provide even PAR readings without premature burnout. Many inexpensive fixtures advertise high wattages, yet produce crappy spectral distribution which wastes energy and starves your livestock. You should of checked this before buying cheap ones.
Lighting isn’t about throwing as much light at your tank as possible. It’s about precision. Get the intensity and wavelength mix dialed in for your particular inhabitants, and the rest will take care of itself. Healthy organisms beat the nuisance ones. The water clears up on its own. Corals open their polyps wider. Plants start to pearl oxygen bubbles. There you have it, that clarity is the real reward for getting the spectrum right.
