Why are there so many plants looking anemic? Why is glass covered in algae? More likely than not, its got nothing to do with how good the bulb looks from across the room. What’s actualy going on is what happens underwater, i.e., how much usable light (PAR) reaches substrate.
Illumination is viewed by most aquarists as a binary switch; it’s either on or off. Lights gets purchased according to watts or aesthetic preferences. This is where most people miss the mark. Aquatic organisms functions on precise levels of energy, not general amounts of light.
How to Use Light Correctly in Your Aquarium
These numbers are too big. So I broke them out into more workable areas on this chart. As you can see, it shows exactly how much light your tank recieve. Knowing what zone you’re in will alter the way you grow plants as well as manage your water chemistry.
Plants such as anubias or Java Fern is fairly easy plants that thrive in the low to medium-low light range. You do not need special fertilizers or CO2 injection. These plant do fine and you won’t have to baby sit your tank every day. They make great plants for a beginner who wants a living piece of aquaria but doesn’t want to fuss with it every day. The graphic puts all these durable creatures in one group visually, this reminds you that things can be kept simple here.
As you push further into the high-light zones, things can become complicated. Adding expensive lighting fixtures with no support for the resulting biological demand are how hobbyists can get themselvess in trouble. Plants like red stem varieties or carpeting foreground grasses is voracious plants that eat lots of energy. They need plenty of fertilizer and carbon dioxide to turn that energy into plant growth rather then food for algae. If there aren’t sufficient nutrients, the excess light will fuel blooms of cyanobacteria or hair algae. This is a classic example of too much input and not enough processing power in the biological system.
Besides brightness, when do you turn them on? How about how long they are lit? A predictable day/night cycle will help plants develop a solid circadian rhythm which supports even plant growth while reducing stress. Eight to 10 hours per day is typical in many successful tanks. It gives them plenty of time for photosynthesis without providing a chance for algae to reproduce.
More sophisticated tank keepers also play around with siesta lighting schedules where they divide their daylight period into two blocks with a period of darkness in between. Such interruption deprives light-loving filamentous algae of constant light and potentially starves them out. Plants gets a chance to recuperate and grow again during their second block.
Because light gets scattered and absorbed rapidly in water, depth matter quite a bit. What light level is at the water’s surface is not necessarily the same as what reaches your substrate. For example, half of all available light energy can be lost in only fifteen centimeters of water in a freshwater tank. So that fancy fixture looks good from overhead but sends out very little light to anything below it on the gravel. Always measure light levels where your corals/plants resides. Knowing this makes the difference between guessing and knowing.
It’s all more important for a reef tank where corals house symbiotic algae responsible for their coloration and well being. Stony corals such as small polyps wants the same kind of intense light seen in shallow tropical lagoons. Strong blue spectrums suits them best. Soft corals prefer moderate intensity placed lower in the tank. Match the type of coral to where it grows vertically and each one will get what it needs without shading out its neighbors.
At the end of the day, keeping an aquarium is all about finding that balance, the balance between flow, nutrients, and light. High light means you also need high nutrients and plenty of carbon dioxide. A complex ecosystem require knowledge based off the flow of energy through water. When you stop guessing (i.e., using your eyes to visually estimate light) and begin measuring actual number of photons being produced, the mystery fades away.
Your tank isn’t this mysterious black box anymore. Instead, it becomes a manageable, predictable environment. The corals pop with color and the plants grows green. Algae is kept in check because you finally provided each organism precisely what it asked for.
