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If you’re setting up a planted tank or upgrading to an aquarium with LED lights, one question almost every hobbyist asks is: How far should the lights be from the water surface?

This may appear to be basic, but this distance influences three important factors: how well plants will grow, how easily algae will be controlled, and how happy your fish will be. When this distance is correct, it can be the key to moving between a lush, blooming tank and one that is struggling to keep clear of green algae.

Why Light Distance Matters

In planted aquarium lighting, you want to make sure that you are not just pumping out a lot of light but that your plants can actually utilize that light effectively. If your lights are too close to the water, the high intensity could cause your plants to " burn" or grow too fast, leading to algae, and the fish may hide in stress. Also, some plants will lack color and may be bleached if it is too bright for them.

If your lights are too far from the water, your plants will start to slow down due to a lack of light intensity. Low-light plants will start to " stretch" and lose color, and high-light plants may be stunted, or the colors may become faint. What you really need is optimal, efficient light, not the brightest light.

Recommended LED Distances for Planted Aquariums

Since most hobbyists will have LEDs nowadays, I'll put a brief guide to common arrangements. Standard LED plant lights can be about 15-30cm above the water's surface, High-output High PAR LEDs can be about 25-45cm above the surface, low-light plants (Anubias, Java fern etc) will often be fine with 20-35cm from the surface and high light plants (carpetting plants, red ludwigia) will want to be around 15-25cm from the surface. Basically, with higher power LEDs, the greater the distance they need to be to deliver sufficient energy to the plant.

A Real-Life Example

Almost every hobbyist will be familiar with this experience. You get a stronger LED lamp and hope your plants will grow more rapidly. In a week, the glass and the leaves are already covered with green algae, the tips of your plants turn yellow, and your fish disappear in the corners. After the lamp is raised from 10cm to 25cm above the water, and the light switches off 4 hours earlier, your tank is slowly restored. After 2 weeks, the algae are gone, new growth can be seen, and the fish are no longer so withdrawn. This shows it is often the distance and the duration that are the most important, and not the intensity itself.

Tips for Using LED Lights in Planted Tanks

With LEDs light control becomes more important. New tanks only need 6-7 hours of light each day, but once established, they do best with 7-9 hours. Lights that are left on for 10+ hours are generally bad because they will cause algae to grow, and the plants won't be very healthy.

Different plants have different light needs as well. Low-light plants will do fine farther away from the light, medium light plants do well at the regular suggested distance, and high light plants will need closer light and a stronger output to keep growing and to stay colorful.

It also helps a lot to have a light with a height-adjusting stand. If the stand is stationary, the distance will change as your plants grow.

Common Mistakes to Avoid

An easy trap for new fishkeepers to fall into is the idea of "the brighter the better", and upgrading without changing the light height, or forgoing the duration and timing aspect, along with having lights too close, to promote algae. Another frequent oversight is increasing the light height as the plants get larger. For a truly successful planted tank, consistency and equilibrium are more crucial than simply more intense light.

FAQ: Quick Questions About Light Distance

Some questions appear so regularly that they really ought to have their own short FAQ. Is it okay to place the best planted aquarium lights directly over water? No, you shouldn't. Your fish could become stressed, your leaves on your plants may get singed, and you will most likely cause an algae outbreak. Keep around 15cm above water unless the light source is extremely low-intensity.

Your plant's growth is stunted for whatever reason. The most likely cause is the distance between the light and the plants, or there isn't enough light. The cause will usually be a lack of PAR. Will my low-light plants grow okay with high-intensity lighting? They will grow; you just need to monitor them to ensure they don't turn yellow or melt from the high intensity and too many hours.

Final Thoughts

So, how close should aquarium lights be to the water? For planted LED lights, start with 6-12 inches, then adjust according to which plants you have, how many watts the light gives off, and if you have a substantial amount of algae or not. When these are combined with proper light cycles, you should achieve the best results. The right placement distance is not a generic "normal distance," it's based on your own tank and not a generic one.

If you are looking to consider a top-mounted light fixture or lights to sit above the tank, our Seaoura Aquarium Lighting Guide can help both by recommending products and by guiding you in proper setup, depending on the plants you plan to have. Get the light, get your planted tank healthy and happy, and your fish will appreciate you!