PAR Levels for Corals (SPS, LPS, Soft Corals)
Mastering the correct aquarium lighting in a coral reef tank is essential. One of the first steps is to understand how light levels are measured, this is where PAR (Photosynthetically Active Radiation) comes in. Different coral species have evolved best in certain light habitats, therefore, it is essential to tailor your aquarium lighting setup to meet your coral collection’s needs.
What is PAR (Photosynthetically Active Radiation)
Before we get into the specific requirements, you should understand what PAR actually measures. PAR measures the intensity of light and the wavelengths that corals and their symbiotic algae can utilize for photosynthesis. PAR levels are measured between 400-700nm, and each coral species has a specific PAR range.
PAR is typically expressed as μMol/ m²/s and often shortened to “micromols” or “PAR” in the aquarium hobby.
While lux or lumens measures are often used for human visual perception, PAR quantifies the light energy available to corals specifically. This difference makes the type of PAR meters an essential aquarium equipment for serious reef aquarists who want to optimize their tank conditions.
PAR Levels For SPS Corals
Most Small Polyp Stony (SPS) corals such as Acropora, Pocillopora, and fast-growing SPS corals like Montipora live relatively high up in coral reef formations where light is most intense. Over millions of years, SPS corals have adapted to high light environments and typically need the highest PAR levels in reef aquariums.
Below are the recommended PAR level requirements for SPS corals:
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Acropora: 200 – 300 μmol/m²/s
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Montipora: 200-300 μmol/m²/s
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Pocillopora: 250–350 μmol/m²/s
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Stylophora: 300-400 μmol/m²/s
NOTE: These are recommendations, however some SPS corals have species specific requirements. For example, some Acropora corals can tolerate PAR levels up to 700 μmol/m²/s and some Montipora corals thrive best between 400 and 450 μmol/m²/s.
Finding a sweet spot for SPS corals is really important, as under low lighting conditions, SPS corals can exhibit slow growth and paler colors, and if the lighting is too intense the corals can start bleaching or lead to tissue recession or coral diseases. When introducing corals to a high PAR environment, you should always do it gradually over weeks to allow the SPS corals to acclimate.
PAR Levels For LPS Corals
Large Polyp Stony (LPS) corals such as Euphyllia, Trachyphyllia, and Favia species are commonly found in the mid-regions of coral reef systems. These corals generally have larger polyps, and many of them are very capable of catching food, making them less dependent on photosynthesis for energy like SPS corals.
Below are the recommended PAR level requirements for LPS corals:
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Euphyllia corals (Hammer, Torch, Frogspawn): 100-250 μmol/m²/s
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Lobophyllia corals: 150–200 μmol/m²/s
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Trachyphyllia corals: 50-150 μmol/m²/s
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Favia and Favites corals: 50-150 μmol/m²/s
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Acanthastrea corals: 100–250 μmol/m²/s
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Blastomussa corals: 75-125 µmol/m²/s
Many LPS corals can adapt quite well to different light conditions, although they still do well under stable and proper lighting. If LPS corals receive too much light you may notice polyp retraction during maximum light hours, whitening of upper surfaces, or unusual corral coloration. If they do not receive enough lighting, LPS corals will start to decrease, and you may notice the corals "reaching" up or becoming sluggish over time.
PAR Levels For Soft Corals
Soft corals, such as Zoanthids, Mushrooms, Leather corals, and Gorgonians, have adapted to low-light environments, however, some soft coral species like Gorgonians are capable of thriving at surprisingly high PAR levels.
Below are the recommended PAR level requirements for soft corals:
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Zoanthids and Palythoa corals: 50-150 μmol/m²/s
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Mushroom corals: 50–150 μmol/m2/s
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Leather corals (Sarcophyton, Sinularia): 100-150 μmol/m²/s
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Kenya Tree Corals: 80-250 μmol/m²/s
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Xenia corals: 100–150 μmol/m²/s
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Gorgonian corals: 100–250 μmol/m²/s
Studies have noted that some soft corals have demonstrated phenotypic plasticity to cope with different light environments. This allows the corals to change their physical characteristics without changing their genetic makeup. This is why many hobbyists believe that they can adapt in a wider PAR range. However, remember to always gradually increase PAR levels when first introducing corals into your reef aquarium.
PAR Considerations in aquariums
Knowing PAR requirements is just one part, but to truly provide the best PAR level for your corals, you have to know how to measure it in your aquarium.
Important aspects to keep in mind when measuring PAR:
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PAR drops rapidly with water depth. So, measure at the depth that the corals are placed in the aquascape.
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Light is most concentrated directly below light fixtures and less toward the sides of the tank. If you have corals spread across your aquascape, you may need to add multiple fixtures so that the light reaches multiple points in your aquarium.
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Light reflects off different surfaces such as live sand, rocks, and even tank walls, creating potential “hot spots” of higher light intensity.
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LED output decreases slowly over time, and the bulb spectrum changes over time. Typically, bulbs will need replacing every 6-12 months to maintain optimal PAR levels.
Light Zones in reef aquariums
Instead of trying to achieve uniform lighting across your tank, most hobbysists create lighting zones. By using uniform lighting in different regions and by carefully arranging corals, you can house various species in one aquarium system.
We recommend creating the following coral zones:
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Upper zones: SPS corals
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Middle zones: Most LPS corals and light-happy softies
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Lower zones: For lower PAR LPS corals and soft corals
The Best Aquarium Lighting For Optimal PAR Levels
PAR measurement is essential to the success of a reef tank, but the story doesn’t end there. Light, more specifically the level of blue, white, and red wavelengths in the light spectrum, greatly influences coral growth and color.
Transitions from light to dark are really important, too. In the ocean, coral reefs experience slow periods of light during sunrise and sunset instead of hard on/off cycles. Aquarium lighting that has programmable features can mimic these natural transitions and minimize stressful shock responses in sensitive coral species.
Below are our favorite lighting fixtures for aquariums:
Conclusion
One of the most crucial aspects of aquarium maintenance is aquarium lighting. Whether you have low-light corals or coral that enjoy more intense lighting, it is key to understand the PAR requirements for your specific corals so that you can create an ideal environment for them to grow and thrive.
If you are unsure what PAR levels your corals need or what lighting fixture is best for your aquarium setup, contact the Reefco Aquarium’s Team today.
