Freshwater Aquarium Lighting Time

With our lights in place, fish happily swimming about and plants fully situated our tanks are finally launched. Later we add on a light timer so that we no longer have no light days or days without a night. Now the question is how your fresh water aquarium lighting time should be distributed.

If you’re not looking into details the best schedule to use is 8-12 hours a day. I’ll explain more specifically the time is adjusted for later on.

For those new to the hobby I will first explain the benefits of proper aquarium light timing as well as the pitfalls of careless light usage.

The Benefits Of Correct Freshwater Aquarium Lighting Times

Using the right freshwater aquarium lighting time will often give us a plethora of benefits such as:

  • Accelerated plant and coral growth
  • More colorful plants, corals and fish
  • Save on electricity
  • Being prepared for vacations

The last one is something I must stress. If you have someone house sitting your fish make sure they either know the lighting schedule or have a timer. One of my house sitters thought the window was enough light. When I got home and flipped the light on my Clowns had a ghostly face on them with faded colors. My mandarin even hid for the rest of the day, making me think he had been eaten by my coral banded shrimp. Luckily as everyone warmed up to the light they returned to normal.

When your plants, corals and fish have more color it is because they are healthier and less stressed. Many corals will even extend further under perfectly regulated lights where as plants will maintain the right color and avoid any sun burns extended lighting can cause.

As a result of the better health the plants will be able to soak in more light, grow faster and remove more toxins from the water. Corals will do the same, but are sometimes limited by the nutrients in the water.

Finally saving on electricity is simple. if you cut say 2 hours of lighting off a day it is about the same as turning the light off for 91 days. Needless to say this is a huge chunk of our electric bill saved.

Picking The Perfect Freshwater Aquarium Lighting Time

If like me you first tried to regulate the lights time on your own we should be on the same page. Bottom line is it is next to impossible. We are not robots and do not wake up and go to bed at the same time every day. Likewise we cannot adjust our light at the right time every day for years. It just isn’t possible. So for this guide I will be speaking as if you own an aquarium light timer.

First off we must note that aquarium lights should not be on as long as we are awake. 14-20 hours of light is just too much for most tanks. Instead we will be shaving off the times when we view our tank the least.

The best time to turn our aquarium lights on is not when we first wake up. The first thing we do when we get out of bed is often shower, eat or sleep a bit more. None of which we will be looking at the tank. By waiting this hour we have already taken off one of the hours we need to secure a better lighting schedule.

If you work early in the morning you may even choose to have your lights turn on a few hours after you start working. I personally don’t recommend leaving the light off until say 2pm but keeping the lights off until 11am means the lights are able to stay lit until 7pm to 11 pm.

This brings us to the next point of planning your freshwater aquarium lighting time. Depending on where the tank is located you may need the lights to be off earlier. For instance my small saltwater tank is located in the bedroom. Keeping this light on until 11pm is nice some days, but when I need to sleep early it is far from ideal. This brings me to my biggest point:

Schedule your light around your average day, not your ideal day!

having the tank off early on my day off may not be as fun as keeping it on until 11, but it sure beats having bad sleep or cutting my corals short on their lighting.

Specific Freshwater Lighting Problems And Solutions

This is where I will explain the range of 8-12 hours being the best aquarium lighting time. As many have learned not all aquariums are the same. For example my neon tetra tank will have far less waste in it than a goldfish tank. This is both because my tetra tank is under stocked and goldfish in particular are messy eaters.

Why does this affect my aquarium lighting times?

Simply put, algae. The green, weedy algae that will plague every new aquarists tank along with brown diatoms that cover sand beds. This stuff loves two things. Nutrient rich waters and excess lighting. Combining the two is just begging for an algae bloom. This is why for nutrient rich tanks or tanks that are often over fed should only receive 8 hours of light. This gives plants and fish enough light to stay happy while limiting the light algae has. This alone will not stop the algae, nothing can do that, but it does slow it down to a manageable rate.

The middle ground, about 10 hours, has several uses. Typically it is used as the safe bet on lighting times when the aquarist does not know enough about their tank to make an informed decision. This is fine as no one comes into the hobby knowing everything. For those who own tropical fish, the most abundant kind of aquarium fish, 10 hours also helps to simulate their natural day times. Combine this with timers that slowly turn the lights on for the best effect.

The longest stretch of the range, 12 hours, is best used by those growing plants or corals. Most plants and corals only need 8 hours of light to stay healthy, but will happily accept more light. In fact many coral dealers never switch off their lights but instead swap to a low strength blue light over night. If you own any fish this is not recommended.

The biggest issue with 12 hour lighting periods is that the algae and plants/corals will be competing for the nutrients in the water. At first this often results in the algae winning out, causing an algae bloom. However as the corals and plants grow, the tide of the battle turns and less and less algae grows. Eventually having the 12 hour lighting period will result in the same or even less algae growth than sticking with 8 hour light periods would.

The last element to consider when choosing your freshwater aquarium lighting time is its location in your house. Many new to the aquarium hobby will often place their tank in front of or across from windows, resulting in large amount of natural light that pours into the tank. This combined with artificial lighting can cause constant algae blooms that are hard to beat. If the tank is small enough I suggest relocating it, however some tanks will never be moved once they are filled with water. Thick curtains are your friend here, as are heavily planted tanks.


For those who are new to the hobby try setting your lights to 10 hours of light a day. Adjust to less light if you have rapid algae growth or add more light if you see low algae growth and wish to grow plants.

If you are constantly seeing algae reduce the lighting time as well as blocking out any natural light produced via windows or reflective floors. With all these elements in play your freshwater aquariums lighting time should quickly be established, reducing algae, saving money on electricity and making all your tank inhabitants happy.

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