How Long Should Aquarium Lights Be Left On?

Use a Timer to Give Your Fish and Aquatic Plants the Right Amount of Light

Cat looking at fish tank
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The ideal photo-period, or length of time the aquarium lights are on ranges from eight to 12 hours, depending on the aquarium setup. Generally, 10 hours a day is a good average for most aquariums.

When Should You Reduce the Aquarium Light Time?

If algae is a problem in the tank, a contributing factor is usually too much light. Reducing the time the aquarium lights are on to eight hours, or a bit less if necessary, will help reduce the algae growth.

Some fish prefer lower lighting conditions. Many cichlids thrive on less light, as do many species of the tetra family. If the room has good ambient lighting, it's possible to reduce or even eliminate additional aquarium lighting.

When Should You Increase the Aquarium Light Time?

If there are live plants in the aquarium, the aquarium lighting period should be increased. Plants require as much as 12 hours per day, however, the time will depend on the aquarium setup and species of plants.

Use a Timer for Your Aquarium Light

The biggest obstacle in maintaining uniform aquarium lighting is that owners aren't able to turn the lights on and off at the same time each day. Fortunately, there is an inexpensive and easy way to remedy that problem.

Purchase an inexpensive timer and plug the lighting unit into it. Set the on and off times to obtain the desired period of light, then cross that task off your daily To Do list permanently.

Light timers are highly for all aquarium owners.

Aquatic Plants in Your Aquarium

A very important reminder about true aquatic plants: They must be kept wet at all times. If they are even allowed to partially dry when transplanting new clumps, these plants may suffer for weeks, or even die.  Also, do not remove live plants and clean them under running water; this will damage, break or even kill live true aquatic plants.

The almost microscopic whitish slime like layer on plants is actually good bacteria—the fish eat it from time to time—and it is part of the nature of the plants, part of what keeps an aquarium in homeostasis.

To get the best looks out of your plants, plant them in the substrate and ensure they are well anchored to the bottom of the aquarium. Planting in thickets (bunches or clumps) is the most eye-catching, but don't use too many plants in a thicket or clump. The plants need room to grow and get full light on all the branches and leaves of the thicket or clump. As long as your fish can swim cleanly around and through your aquarium plants, you are not overcrowding your aquarium with plants.

You can increase the number of plants in your aquarium, if you have proper lighting and water conditions, in one of two ways. (Well, there is a third way—you can buy more—but let’s talk about propagating the plants you already have). Vallisneria and similar plants send out runners under the substrate, which in turn send up little versions of themselves through the substrate, next to the parent plant. These runners can be cut apart and each little plant is a new plant unto itself that can be transplanted elsewhere or left to grow where it sprouted.

Leave the Aquarium Light on Longer for New Plants and in Winter

When you introduce new live plants to your aquarium, it is best to leave the light on for longer periods of time; this gives the plants a better chance to take root. If you begin to see excessive algae, shorten the periods of light, this will retard the algae growth. It is also good to leave the aquarium lighting on longer in the winter, when natural light is less due to the season, for best growth and the healthiest aquarium plants.