The differences in Aquarium Lighting
Every aquarium is different based on what you want to achieve with your aquarium. Three of the most common types of aquariums, in which affect your lighting requirements are: planted freshwater aquariums, hard/soft coral saltwater aquariums and fish only aquariums. Each of these aquariums requires a different Kelvin, wattage and duration of light exposure.
Freshwater Planted Aquarium
The freshwater planted aquarium requires very specific lighting to grow plants. Fish only need anywhere from 7-8 hours of light a day. The plants however prefer a photoperiod of 8-12 hours per day. Every plant has a different duration in which it photosynthesizes. Most plants will stop photosynthesizing after that 8-12 hour period. This means the plant and the aquarium are not benefiting from the light anymore. In fact, the light on past 10-12 hours will greatly increase your risk for stressed out fish, rampant algae growth and stunted growth for your plants.
Most people know that the lights must be turned off at some point in time so the fish can rest. This is the same for plants. When the light is on the plants will photosynthesize anywhere from 8-12 hours depending on the plant. When they photosynthesize the plants will reduce nitrogen, produce oxygen and absorb c02 in order to grow. When the light is turned off the plant will stop photosynthesizing and instead of creating oxygen and absorbing c02 and nitrates, the plant will actually do the opposite. Plants absorb oxygen in the water during night time.
When picking out a light in a freshwater planted aquarium the it is suggested to have at least one watt per gallon of water in the aquarium for LED lighting. If you have standard fluorescent lighting you will need anywhere from 3-5 watts per gallon. LED lighting is becoming much more affordable and tends to be more efficient as well. Putting more than 3 watts per gallon(LED) or 5 watts per gallon (fluorescent) in your aquarium setup is most likely too much unless you have a very deep or wide aquarium. More than the recommended amount of light will increase the chance of uncontrollable algae growth.
A huge factor of lighting is the degrees Kelvin the light is rated at. Kelvin is a scale we use to measure the temperature/spectrum of the light. The spectrum for a planted aquarium should be around 6700 Kelvin for most freshwater plants. Getting a light with a lower Kelvin than 6500 is bound to create algae problems sooner or later. Anything more than 7000 would not be a warm enough light to maintain most freshwater plants.
Fish Only Aquarium
Fish only aquariums are very easy as far as lighting is concerned. When choosing a light for a fish only aquarium it is okay to look for a light that will cost you less money. When dealing with a fish only aquarium the lights can be left on for 6-12 hours. Most fish don’t stress until the light is left on for a duration of 14 hours or longer. Leaving any light on over 14 hours a day is almost certain to grow undesired algae.
For an aquarium containing just fish it’s best to go with a light that will cost you less in electricity and bulb replacement. LED lighting is expensive upon purchase but will save you money in the long run in electricity and you don't need to replace the bulbs nearly as often. Less than 1 watt per gallon is ok in an unplanted aquarium for LED lighting. For standard fluorescent bulbs, 1-2 watts per gallon is appropriate.
The spectrum of lighting in your fish only aquarium is not a concern for the fish. Pick out the light that looks the best for you. Lower Kelvin lights with more of a red spectrum tend to grow algae whereas a higher spectrum light will have less of a problem growing unwanted algae in your aquarium.
Saltwater Reef Aquariums
Live reef aquariums are very particular when it comes to lighting. A reef aquarium light should be left on 8-12 hours a day depending on the corals you have in your aquarium. It is hard to say how long a light should be on for because in the ocean these corals grow in the spot that gives them optimal lighting. Optimal lighting is different for every coral so you have to figure out what suits your aquarium the best.
Saltwater aquariums are expensive. The light will be no exception. A living reef in your aquarium will require over 5 watts per gallon of standard fluorescent lighting. Be very careful with LED lighting in a saltwater aquarium. Half a watt per gallon is plenty for a lot of aquariums. The deeper or wider your aquarium is you may need anywhere from .5 watts per gallon to 2 watts per gallon LED. LED lighting can cause your coral to bleach. Make sure you dim your LEDs down when adjusting your coral to the new lighting. If your coral starts to bleach at all turn the LEDs down immediately.
Saltwater reef tanks have a wide range of light spectrums. The most common and effective lighting for corals is the 12,000K + 445nm Royal Blue. This spectrum promotes healthy coral growth, keeps your coral bright in color, penetrates the water well and makes your fish and corals “pop”. If you don’t have live coral don’t waste all your money on an expensive light. These lights are designed to grow coral and are very expensive.