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Hydra 32HD versus Hydra 64HD? Will multiple Hydra 32's perform as well AND save you money?

The Aqua Illumination Hydra 32 is essentially half the size and power of the Hydra 64 fixture, but does that mean it can only do half the work?  In this episode, the BRStv Investigates crew compares the PAR data to find out if the Hydra 32 measures up to its old brother, the Hydra 64.  In addition to comparing these flagship lighting solutions from AquaIllumination, we explore the ideal mounting height, fixture spacing, and spectrum settings you need to hit the ground running with your brand new Hydra 32!

How Many AquaIllumination Hydra 32 HD LED Do I Need?

The best path to choosing an effective reef tank LED is to first decide your particular tank goals, then choose a light that can supply those lighting conditions inside your specific tank dimensions. As it pertains to reef tanks, the most common tank goals can be split as follows based on the type of coral you plan to keep. The key to achieving the lighting conditions is to follow the recommended mounting heights, fixture spacing, and output settings we found during our tests.

LPS and Soft Coral dominant aquarium - medium to low light conditions (75 - 150 PAR)

  • 60 Gallon 24" x 24" aquarium = 1x Hydra 32HD LED Light
  • 120 Gallon 48" x 24" aquarium = 2x Hydra 32HD LED Lights

SPS and stony coral dominant aquarium - high light conditions (200 - 300 PAR)

  • 60 Gallon 24" x 24" aquarium = 1x Hydra 64HD LED Light
  • 120 Gallon 48" x 24" aquarium = 4x Hydra 32HD LED Lights

Best Mounting Height for AquaIllumination Hydra 32 HD

The lens design on the latest Hydra series fixtures is a major improvement over previous models because it blends the diodes better and produces a much more even spread of light when mounted correctly. This means you can more effectively cover a larger area without creating significant hotspots and is one of the major reasons the Hydra 32 is such capable LED light.

We tested the Hydra 32 over a 24" x 24" area and measured the light spread starting at 6" from the water's surface which produces a significant hotspot and drastic drop in PAR around the outer edges. As we move the light higher off the water's surface, we start to see a dramatic improvement in that spread of light.  After testing inch by inch, we finally found the optimal mounting height to be just 2" higher than the larger Hydra 64 HD.  At 14" from the water's surface, the Hydra 32 HD produced the most even spread of light across a 24" square area with less than 15% light loss outside of the tank. 

Based on our lighting tests, the best mounting height for the Hydra 32 HD is 14" from the water's surface.

Mounting Configuration and Fixture Spacing

Over a 24" aquarium, a single Hydra 32 HD should be mounted dead center to provide that even spread we previously tested at 14" from the water's surface.  When we look at a 48" aquarium, the spacing becomes even more important to optimize that spread and cover the entire aquarium with sufficient PAR. 

We took a plethora of PAR readings over our 48" 120-gallon aquarium to find out exactly how you should configure x2 and x4 Hydra fixtures to achieve the best possible spread.  We define the best spread using the same criteria where we find less than a 15% light loss between the center-most PAR readings and the outer ring.  In both scenarios, the fixtures are all mounted at 14" from the water's surface. 

LPS Hydra32 HD Light Spacing

SPS Coral Hydra 32 HD Light Spacing

While it might seem logical to space the LED fixtures evenly over the top of your aquarium, the intersection of the light spreads and reflections off the tank walls creates an uneven spread with areas of extremely high and low PAR values.  By spreading things out and using those light spread intersections and reflections to your advantage, you can achieve a far more efficient spread of light while obtaining sufficient PAR throughout the entire aquarium. 

Spectrum Offering and BRS Recommended Settings

AquaIllumination fixtures are controlled using the myAI app which uses color sliders from 0% - 100% for each of the color channels. They do not provide a suggested spectrum mix rather they provide an "Easy Setup" option which lays out a traditional photoperiod with all channels set to an equal percentage. In order to find the best spectrum, we used a spectrometer to get as close as we possibly could to the tried and true ATI Blue Plus T5 lamp spectrum that has years of proven results over reef aquariums. 

ATI Blue Plus vs BRS Recommended Hydra 32 HD Spectrum Settings
BRS Recommended Hydra 32 HD Settings

We want to create the widest band in the blue color spectrum as possible and found the following settings to produce that ideal color spectrum using the Hydra 32 HD. Keep in mind that this would be the maximum possible while still maintaining the ideal color spectrum we found using our spectrometer. 

  • UV: 110%
  • Violet: 110%
  • Royal: 120%
  • Blue: 120%
  • Green: 10%
  • Red: 10%
  • Moonlight: 0%
  • Cool White: 60% 

We provided our recommended settings below for the 60-gallon cube and 120-gallon aquarium we used during our testing using this spectrum ratio. Using a PAR meter is the only way to really know that you're providing the ideal PAR levels in your tank. In order to maintain this spectrum and reduce the output, simply maintain the ratio across all color channels and drop them incrementally.  For 10% less output across the board, drop each channel by 10% while still maintaining this ratio. 

BRS Recommended Photoperiod

In terms of photoperiod, we recommend the following simple parameters which have proven successful over our own tanks here at BRS. You can adjust the exact time of day based on your own personal preference and we simply recommend adjusting so that you can enjoy the light of the aquarium while you are normally home. 

  • 9 hour peek photoperiod
  • 30-minute ramp up and ramp down
  • Total of 10 hours of light. 

Below you will find real-world settings we would recommend for using the Hydra 32HD over the two tanks we tested.  These produced the ideal PAR ranges for both an LPS and SPS-dominated tank where more than 75% of the tank was within the recommended PAR zones. In all cases, we maintained the above Ratio for spectrum, and simply adjusted all of the channels based on the PAR readings required for each tank type. All fixtures were mounted using the 14" height and recommended fixture spacing as well.  

BRS Recommended Settings For LPS and Soft Coral Dominant Tank

60 Gallon Cube - 24" x 24" (1x Hydra 32HD)

  • UV: 88%
  • Violet: 88%
  • Royal: 96%
  • Blue: 96%
  • Green: 8%
  • Red: 8%
  • Moonlight: 0%
  • Cool White: 48% 

120 Gallon - 48" x 24" (2x Hydra 32HD)

  • UV: 66%
  • Violet: 66%
  • Royal: 72%
  • Blue: 72%
  • Green: 6%
  • Red: 6%
  • Moonlight: 0%
  • Cool White: 36% 

BRS Recommended Settings for SPS Dominant Tank

60 Gallon Cube - 24" x 24" (1x Hydra 32HD)

  • UV: 110%
  • Violet: 110%
  • Royal: 120%
  • Blue: 120%
  • Green: 10%
  • Red: 10%
  • Moonlight: 0%
  • Cool White: 60% 

120 Gallon - 48" x 24" (4x Hydra 32HD)

  • UV: 88%
  • Violet: 88%
  • Royal: 96%
  • Blue: 96%
  • Green: 8%
  • Red: 8%
  • Moonlight: 0%
  • Cool White: 48% 

Can the Hydra 32 HD Outperfrom the Hydra 64 HD?

We found that the Hydra 32 HD is the perfect solution for LPS and Soft Coral aquariums. One fixture for every 24 cubic inches of tank area will provide sufficient PAR throughout the entire aquarium for almost any rectangular aquarium.

If SPS corals are your forte', you can likely save some money in fixture costs by simply using more of the smaller Hydra 32 HD. Over the 48" tank, we found that using 4x Hydra 32 HD provided up to 15% better performance and coverage compared to using 3x Hydra 64HD fixtures because we were better able to configure the smaller light fixtures over top of the aquarium. This results in a savings of over $500 and better performance! 

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