Metal Halide Mounting height

[Hurricane Aquatics]

Hey all,

As many of you know, I've had my full Acropora tank running for about 9 months now with great success. About 2 weeks ago, out of the blue, I started having issues with PE, RTN, etc. I'll get into that another time and what steps I've taken.

I have the 36 inch Reef Brite MH 250w that has two 250w DE bulbs and using Reef Brite 250w electronic ballasts. I was supplementing with 2, 36 inch illumagic Blaze leds. During my issues, I turned off the halides and ran only LEDs, adjusted for PAR to be the same as with halides.

Tonight, I was messing around with my Reef Brite MH and out two new Hamilton 20k bulbs in. I turned off the LEDs and lowered the MH fixture to adjust for PAR. I was first surprised and then very curious.

Here are the needed information. MH fixture mounting height was 7 inches (glass panes) from the water surface. Acropora were positioned about 12 inches below the water surface. Water is 20 inches deep total.

New bulbs that had only been on about 10 minutes were reading 460 PAR. I was surprised by that with 20k bulbs. I let the bulbs warmup for about 30 minutes and the brightness visually dropped. Same height after 30 minutes, PAR was reading 284.

That seems very low to me. I would think with the fixture dropped that low to the water that I would be getting much higher PAR. Of course the reading was taken 12 inches under the water. Sound right to you?

Pics below, disregard messy tank, still cleaning up after some issues.

 

[Bpb]

That is low. I was getting 300+ at 24” depth with 12” fixture height (36” distance from base of reflector) with my 250 watt Hamilton 20,000k bulbs. This was directly under the fixture. On the top of the rocks it was 500-600

 

[A. grandis]

Hey all,

As many of you know, I've had my full Acropora tank running for about 9 months now with great success. About 2 weeks ago, out of the blue, I started having issues with PE, RTN, etc. I'll get into that another time and what steps I've taken.

I have the 36 inch Reef Brite MH 250w that has two 250w DE bulbs and using Reef Brite 250w electronic ballasts. I was supplementing with 2, 36 inch illumagic Blaze leds. During my issues, I turned off the halides and ran only LEDs, adjusted for PAR to be the same as with halides.

Tonight, I was messing around with my Reef Brite MH and out two new Hamilton 20k bulbs in. I turned off the LEDs and lowered the MH fixture to adjust for PAR. I was first surprised and then very curious.

Here are the needed information. MH fixture mounting height was 7 inches (glass panes) from the water surface. Acropora were positioned about 12 inches below the water surface. Water is 20 inches deep total.

New bulbs that had only been on about 10 minutes were reading 460 PAR. I was surprised by that with 20k bulbs. I let the bulbs warmup for about 30 minutes and the brightness visually dropped. Same height after 30 minutes, PAR was reading 284.

That seems very low to me. I would think with the fixture dropped that low to the water that I would be getting much higher PAR. Of course the reading was taken 12 inches under the water. Sound right to you?

Pics below, disregard messy tank, still cleaning up after some issues.

The ReefBrite e-ballast is supposed to use less electricity from the wall than a more "normal" e-ballast. It was made to 'read" the bulb and give the "right amount of wattage" for that bulb. Whatever "reading" it's doing to your bulb, is what's giving the amount of wattage to run that bulb, therefore reflection on your PAR readings. I've heard many stories of that ballast and that was the reason why I've never dropped the buck to try one. But again, so many people swear by it! Your PAR sensor could be the wrong sensor too! That said, the PAR value you are experiencing could be related to a lower than expected wattage going on there. You could call Tullio and chat with him about that.
In any case, the most important aspects of light aren't necessarily the PAR reading!!! The whole aspect of what is emitted is what counts! 20K bulbs will give you less PAR than say 14K or 10K bulbs anyways. Keep that in mind! But that doesn't mean that the 20K bulbs are "weaker". That's why I tell people to forget about PAR using halides!!! PAR measurement is a "fashion" for LED users. To chase the PAR numbers with halides will only confuse you because what the sensor captures isn't the whole picture! That lamp is giving much more than PAR!

In regards to the PE and RTN... Is it really RTN? Or tissue recession at the base? Or bleaching? RTN and STN have more to do with the health of the coral, stress, and excess nutrients in the system. Adaptation to light can provoke stress and trigger RTN, but so can many other things... There is way too many products sold today in the market that shouldn't be used and could provoke stress in our tanks. All about money! Avoid using too many different chemicals and chemical removers. Many times that could be the reason why your corals retract and get stressed. I assume that "PE" means lack of Polyp Extension, and that is also a sign of sress. Good luck!