A Sunny Disposition to Aquariums: The Benefit of Sunlight towards the Planted Tank

There are many arguments behind keeping plants in the aquarium, and most of them tend to center towards one particular rule: 2.5 w.p.g., or “Watts Per Gallon.” If you have a ten gallon tank, that means you putting in 25 watts of light. For a 20 gallon, one would prefer 50 watts of light.

How many watts is your lighting setup?

If it is a normal lighting hood, then chances are that the energy ratio is too poor from incandescent light, and standard fluorescent lighting , while better, is usually still not normally good enough to provide much energy into the tank.

A more professional setup will often use lighting systems that are completely unlike any you would normally expect to see in an aquarium or even at home. Some even use metal halide lights, which are so powerful that they are not unlike the sort of lights theater crews work with: the sort that will burn paint off if left on for too long. The prices for these setups can range from 50 to 400 US dollars at minimum, and this is not including the materials that may be spent installing these stands into the tank or room.

There is another option that most aquarium keepers have that they do not normally remark upon: sunlight. Sunlight, as everyone knows, is used to grow plants everyday. Your plants, being custom-grown to thrive in the particular wavelengths of solar rays from millions of years of natural selection, will gain more from the light than from the glass bulb that they had a few days to acclimate towards.

The Catch?

Of course, most experienced fish owners are well-aware of sunlight. In fact, there is almost a sort of taboo towards it for the things it can do. For example:

  • The concentration of light that the sun gives out can be intense: too intense for any normal aquarium. It will tamper with the temperature of the aquarium depending on how strong the sunlight is and for how long it exposes the aquarium. For larger aquariums it will not be as much of an issue, but for smaller ones where the amount of water displacing the heat is very little, it can be fatal.
  • Excessive light will bring algae out in hordes. Like a pool of tepid rainwater, algae will photosynthesize rapidly from the nitrates in your tank and the readily-available sunlight. Plants might even end up growing the algae off of them, forcing them to eventually suffocate and die.
  • Sunlight is not the most consistent thing one can get for a tank. Some days you may get a lot, some days you may get very little. During winter, you are guaranteed to have less opportunity to take advantage of it.


  • Unless your tank is really well-planted, you will almost always have to scrub out algae. Even the best-planted tanks will have a moment where there will be enough glass algae to require a scrubber. Most algaes that are encouraged from sunlight are easy to remove from plants. Green water algae is a nuisance, but only from consistent sunlight exposure; a light fast for a few days (or a rainy day or two) will kill it.
  • While temperature may have been a problem in the past, most modern heaters carry a temperature sensor. If the water does warm from exposure to the sun, then the heater will shut off anyway, saving you the potential trouble of accidentally cooking your fish. A good heater will cost you more, of course, but the difference between a good heater and a good lighting system can go from twenty dollars to much, much, more.
  • Unless the plants you are growing range into some of the most frustrating species, you will not need endless bright light. The lighting setup most people normally have can supplement the plants nicely during the hazier days.


The only time one may see a potential hazard in this decision is if one lives in a warm region with a climate that is already comfortable for the fish. In this case, the heater would likely only turn on during the night, making it worthless during the day, offering no potential thresholds that sunlight would compensate for. And again, the temperature difference will not do much if the tank really is large enough.

Conversely, there are some breeders who, during the summer, will double-line a trash can left outside, fill it with water, a filter, floating plants, and fish. The light does wonders for the fish, the plants grow intense, and the algae that does grow in the can actually offers additional support and even some supplemental nutrition for certain fish. In the end, it still proves to be an invaluable resource when one wants to keep plants but not the equipment for them.