Did Par Test - Am I supernova'ing this tank?

Turd Ferguson

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Mar 23, 2019
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Oakville, On
Curious for some input on the PAR readings of my tank.

I've a 250W (14k Phoenix) above my 40G IMO External (24"L x 24"W x 19"H), sitting about 8" off the waters surface, 7 hour photo period. Since making the transition from T5 I've noticed the LPS and soft corals struggling therefore borrowed a Par Meter from the LFS to get a better idea of how much light I'm hitting the tank with.

Par output, roughly,

Bottom: 250 - 275
Middle: 350 - 450
Top: 600 - 700

Since I've hanged from x4 T5, the SPS which previously seemed rather dormant have come to life although the LPS such as a frogspawn and branching hammer seems to be suffering. The polyps are not as expanded as they usually are, some recession of polyp but they seem to bounce back after a couple of days.

My mushroom corals were doing very poorly, so much that they'd dismount from the rock, float away or move. I've put them in a shady area and things are looking up. Torch coral loves the light (bottom 1/4 of tank), and SPS now have polyp extension and growth. Acans are also shaded and seem fine. Most of the soft and LPS are in the lower 1/4 or 1/3 portion of the tank.

SPS that were dull, now have polyp extension and are colouring up. They currently sit in Middle region of the tank. So in this regard I'm pleased and expect continued growth.

15 Years ago I had x2 150W MH & PC combo over 75G...back then I wasn't too concerned about par, more light the better, blast the tank, if it looked good, continue. I was able to grow everything, SPS, LPS, softies..after year two the tank pretty much exploded with growth. I've read a number of posts, watched video's on PAR but mostly it's relating to LED or T5 fixtures, and the par levels seem far lower than what I'm hitting the tank with.

So my question is, am I blasting the tank with too much light? Once the SPS gets near the top of the tank (top 5-6"), I've measured as much as 800 par (with flow on) No issues with temperature or evaporation. Should I expect issued once the SPS grow towards the top?

Should consider that going forward, the tank will be SPS dominant, and toss the Euphyllia and mushrooms...

Alternatively, can one put a 150 DE bulb in a 250W fixture (Hamilton Cayman Sun)..knowing I'd have to change the ballast for 150W?

First Choice


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May 7, 2015
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Yes you are. No need for anything over 500 and thats on the higher end of the spectrum. Save money on your enery bill too.


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Mar 1, 2016
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Tulsa, OK
Make sure you have plenty of nitrates with all of that light.

What percentage of blue versus white lighting do you think makes the best coral growth combo?

  • All Blue

    Votes: 19 2.7%
  • Mostly Blue

    Votes: 440 62.9%
  • Even Balance

    Votes: 179 25.6%
  • Mostly White

    Votes: 51 7.3%
  • All White

    Votes: 1 0.1%
  • Other (please explain)

    Votes: 10 1.4%