Optimal Hammer Coral PAR Levels

If you struggle with aquarium lighting, you are not alone.

Photosynthetically available radiation or photosynthetic active radiation (PAR) measures the amount or intensity of light that corals utilize in aquariums. 

The hammer coral is a large polyp stony (LPS) coral, which has been a staple for aquariums for decades, therefore they are a must-have coral for every hobbyist. Hammer corals are considered fairly challenging corals because of their living requirements. For example, hammer corals require stable water parameters, moderate water flow, moderate lighting, and supplemental feedings to thrive. 

How Much Lighting Do Hammer Corals Need?

Hammer corals require lighting as a source of nutrition. Did you know inside your hammer coral’s tissues, there are microscopic algae called zooxanthellae? 

These algae have a symbiotic relationship with your hammer coral which means they support each other; your coral provides a safe home for the zooxanthellae, and the zooxanthellae provide your hammer coral with nutrition via photosynthesis. For the zooxanthellae to photosynthesize, lighting is required. 

Your hammer coral only requires moderate lighting for the zooxanthellae to do its job, therefore, a PAR range between 80 and 150 is perfect. 

An optimal PAR of 150 is advised to prevent issues such as coral bleaching, this is every hobbyist’s nightmare, trust me! If your hammer coral is exposed to very high light intensities above its optimal level, it will expel the zooxanthellae from its fleshy tissues, turning white.

On the other hand, if your lighting intensity drops below 80, your hammer coral will lose its magnificent color and it will be starved of nutrients. So, getting the PAR levels right from the get-go is crucial for your hammer coral’s survival. 

Which Lighting Fixture Is Best For Hammer Corals?

Hammer corals grow and thrive under subdued lighting, so sorry to all the old-school reefers, but metal halides are highly not recommended. However, if you are a true metal halide fan, then you can use them, but you must adjust them properly to meet your hammer coral’s PAR and spectrum needs. 

So, what lighting fixture should you get?

LEDs are the best lighting fixture for hammer corals because they will provide your hammer with enough light PAR to penetrate the water, they have the correct wavelengths to promote coral feeding via the zooxanthellae, and they have control settings to mimic natural sunlight which supports optimal health. 

T5s can also be used, as long as the PAR levels are set properly. 

How To Measure PAR Levels?

Photosynthetically available radiation is measured with a PAR meter. It is recommended to invest in a PAR meter to frequently check the lighting in your aquarium, but if you are not quite there yet, most local fish stores (LFS) or online suppliers will happily rent them out for a couple of days or weeks.

A PAR meter will help you check which areas of the reef tank are covered in the right amount of light for your hammer coral to grow and thrive. 

How To Use A PAR Meter?

  • Before using a PAR meter, you need to mount your aquarium lighting the way the manufacturer suggests. 
  • Adjust the color intensity settings required for your type of hammer coral. PAR meters can be used to see your approach’s success and tweak the settings if needed. 
  • Drop the meter into the tank and take PAR readings at different locations and depths in the tank. This will help you with future placements should you add any more hammer corals or any corals for that matter!
  • Once you have finished, rinse the PAR meter and place it back into the box, exactly how it came – these things are expensive so properly storing the meter is very important. 

How Fast Do Hammer Corals Grow?

At first, your hammer coral may not grow very fast, but do not worry it will soon have a growth spurt once it has settled in! As hammer corals are stony corals, they need time to grow their calcium carbonate skeleton. 

Some hammer corals will have visible growth within the first few months, while others may take a couple of years to fully flourish. 

To increase your hammer coral’s growth, focus on the aquarium lighting, particularly the PAR levels. 

Hammer Coral Placement

Hammer corals are pretty flexible when it comes to placement, but, they are best placed in the bottom to the middle region of your aquarium. This can be on the sand bed, on a middle-range rock, or on an island in the middle of your reef tank. 

The most important factor when deciding where to place your hammer coral is an area where its lighting and flow requirements are met. However, you must consider the other corals inside your reef tank, as hammer corals are aggressive. 

Hammers have long sweeper tentacles that contain nematocysts that will sting anything that gets too close, so always allow plenty of space between your hammer coral and neighboring corals. The only exception is when placing your hammer coral next to other hammers or Euphyllia corals. These corals will do fine placed next to each other. 


The hammer coral is a must-have LPS coral in the aquarium hobby. They are fairly demanding in terms of care, but as long as you maintain and provide the proper lighting and water flow conditions, it will thrive! 

Hammer corals require moderate lighting with a PAR range between 80 and 150. To ensure you are hitting your hammer coral’s PAR sweet spot, a PAR meter is highly recommended. 

Getting yourself a PAR meter, whether you invest in one or hire one, is a much better option than the “slide and pray approach”.

  • Roy Lee

    I have an unhealthy obsession with reef keeping and maintaining successful tanks. If you haven't noticed from the website, I love everything related to saltwater tanks like coral, fish, and everything else in between.

1 thought on “Optimal Hammer Coral PAR Levels”

  1. In home aquarium, can zooxanthellae be regenerated in euphyllia corals. (ie Frogspawn, torch etc) Over 3 year period I’ve kept them, slowly losing it’s bright green algae. Tho tissue in all LPS appear to be in good condition the color loss is concerning. Tank cycled about 5 months before adding any livestock. Parameters rarely fluctuate. Lighting under mixed T-5. Anxiously await your feedback.


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