Have MHs on only at end of photoperiod?

[Tang Salad]

I'm getting ready to battle the heat again this summer. Just wondering if there would be any harm in having my photoperiod like this:

Actinics (4x55W) from 11am to 11pm.
MHs (2x150W) from 6pm to 10pm.

I realize the total MH time is quite short. But aside from this, would delaying the brightest lights until the very end of the day cause any disruption of natural photosynthesis cycles?

I keep a mixed reef of SPS, LPS and Zoas. I'm qite sure the LPS and Zoas would be fine, so I'm most concerned about the SPS (Acros and Montis).

MAny tHanKs

[gtrestoration]

It's my understanding that it takes a certain amount of light, duration and intensity before the zooxanthellae get ramped up. After that they'll continue to photosynthesize with considerable less light. I've actually been looking for papers dealing with that issue for days without success.

If that's true then I would think the halides would need to be on first and then deliver less light. Actinic might not be enough to keep them active.

SteveU

[Tang Salad]

Thank you Steve-

That's just the kind of situation I was worried about. Let me know if you can find any more information.

I think it might have been mentioned in Borneman's book of Corals, I'll take a look tonight.

[papagimp]

That would be like giving the corals alot less lighting, In my personal opinion, waste of metal halides and you should find a cooler running fixture. My one tank I have on a MH fixtue I run at night instead of during the day as the rest of my tanks run. Strictly because of heat issues. One tank is turning off as the other is coming on.

[Blown 346]

I wouldnt run the halides less then 8 hours a day myself, otherwise the livestock you keep wont get enought light and will start to bleach and wither away.

[NoSchwag]

Originally posted by Blown 346
I wouldnt run the halides less then 8 hours a day myself, otherwise the livestock you keep wont get enought light and will start to bleach and wither away.

I run my halide 3 to 4 hours a day, if at all. My tank is full of thriving sps.

[nick18tjetta]

On my new tank, I plan on running my halides each 6 hours a day, but not at the same time. EX.

VHO actinics - on at 9am
MH #1 - on at 11 am
MH #2 - on at 1pm
MH #1 - off at 5 pm
MH #2 - off at 7pm
VHO actinics - off at 9pm

I may adjust it so that both Halides are not cranking full force at the hottest part of the day, but you get the idea. I am also switching to electronic ballast and using 175 watt iwasaki aqua2 bulbs to get maximum par with minimal electicity and heat. I will probably still probably have to run the A/C full blast during the hottest part of the day anyway.

[MCsaxmaster]

Given that you'd still be running your actinics, I think you'd probably be ok. You're still providing a reasonable amount of light to the corals just with those.

Also, just a few words on photosynthesis and the saturation of photosynthesis:

People very, very often come to believe or are lead to believe that it takes many hours for the photosynthetic machinery of corals to be saturated with light under constant illumination like we use in aquaria. This is a result of a couple of misunderstandings about how photosynthesis works. In order to actually absorb a photon (or actually, a set of 4 photons) and transfer them through photosystem II and photosystem I takes milliseconds under normal circumstances. Absorption of light takes on the order of 1 * 10 -12 seconds (a billionth of a second). This is the step of photosynthesis limited by light intensity. You see, if you have bright enough light to saturate the coral (or whatever photosynthetic organism) it will take on the order of a billionth of a second for them to reach saturation, not several hours.

In nature the light intensity goes from very low to a maximum as the sun rises. The intensity increases as the sun climbs and eventually the intensity reaches a point that it saturates the corals. The corals take many hours to reach saturation because the light intensity is slowly moving from sub-saturating to a saturating intensity. If you kept a coral covered with a dark box all morning and then took the box off at noon when the sun was out the coral would not take hours to reach saturation. It would reach photosaturation in about a billionth of a second.

So, if your light are bright enough to saturate your corals, this happens as soon as they are turned on (or once they warm up to full intensity, since they are halides).

Now, typically most corals in shallow water produce more photosynthate daily than they respire, though they seem to need this extra for the production of mucus. They also get a lot of energy and material needs from feeding. Some corals can adapt to lower light levels by increasing their feeding efforts while others are less able to do this.

So, having said all this and not really being sure it was at all sensical I'd suggest that shortening the halide photoperiod probably won't result in any real harm to the corals, though calcification will probably slow down. It's better to have slightly lower calcification than bleaching though! I'd experiment and just ensure that whatever you do you're able to keep the temp. from going above 84 F for any length of time. Higher temps can be tolerable, but over 84 F and you're playing with fire.

cj

[nick18tjetta]

I have to say that is probably the best post I have ever read on RC. Can we start a contest for post of the month???

[reefez]

I wouldnt run the halides less then 8 hours a day myself, otherwise the livestock you keep wont get enought light and will start to bleach and wither away.

Totally wrong. Many people here run halides with a short photo period with great success includeing myself. My lfs who has a 300gal. show tank with SPS as thick as your arm and colors to die for runs 6hrs. total light over his tank.

[widefx]

Ditto

I really feel after reading that post I understand more about photosynthesis in corals.

Thank you

[Bonebrake]

Four hours a day is fine. A coral at any reasonable depth in the wild is only going to get four to six hours of saturating light per day and I know several very successful SPS reefers that only run their halides 4-6 hours a day.

[Tang Salad]

Thank everyone very much.

MCsaxmaster- special thanks to you!
That is exactly the kind of information I was needing.

84F, actually 29C, is the absolute upper limit for my tank. This will be the criteria that decides my lighting schedule.

[MCsaxmaster]

double

[MCsaxmaster]

No worries. The question I think is not will this lighting schedule be optimal for photosynthesis and calcification (I'll tell you right now it will not maximize either) but will it be sufficient to keep the animals healthy and growing? I'd answer a reasonably confident 'yes.'

[ATJ]

Originally posted by gtrestoration
It's my understanding that it takes a certain amount of light, duration and intensity before the zooxanthellae get ramped up. After that they'll continue to photosynthesize with considerable less light. I've actually been looking for papers dealing with that issue for days without success.

You have been unsuccessful because there won't be any papers that support that. As MCsaxmaster has explained, there is a direct relationship between intensity and rate of photosynthesis with no delays as such. If there is light, the zooxanthellae can use it. If there isn't any, they can't. Increase light and the rate of photosynthesis increases (until there is enough light to saturate). Decrease the light, and the rate decreases.

[ATJ]

Originally posted by Bonebrake
Four hours a day is fine. A coral at any reasonable depth in the wild is only going to get four to six hours of saturating light per day and I know several very successful SPS reefers that only run their halides

But it is the light before and after saturation that they are using most. While people do get away with short duration for metal halide light it is only because the supplemental lighting is sufficient to more than make up for energy lost in respiration for the rest of the day.

[thriceanangel]

Somewhere there is research saying that after 4 hrs of MH light, you aren't accomplishing much other than raising the temp. Not really but that 4 hours of MH is preferable to more time. I run mine more because I don't use supplementals, and I like to have more than 4 hours to see mt tank.
Not sure about when the 4 hours is though, or if there were supplemental lighting used (I don't think there was) but I think you'll be fine with the MH at the end of the cycle.

[ATJ]

Originally posted by thriceanangel
Somewhere there is research saying that after 4 hrs of MH light, you aren't accomplishing much other than raising the temp.

I don't know about that research, but I can demonstrate that 4 hours per day of metal halide lighting alone will not be enough to sustain a coral long term.

Chalker et al. (1983) published some light saturation data for 2 corals collected at Davies Reef in 1981. The first was Acropora digitfera which was collected from a depth of 1 m (very high light). The other, A. divaricata, was from 40 m (low light).

The very high light/shallow water coral had a respiration rate of -0.70 µmol O₂.h^-1.(mg protein)^-1 (micromoles of oxygen per hour per milligram of protein) and a gross maximum photosynthetic rate of 1.90 µmol O₂.h^-1.(mg protein)^-1. This means the net maximum photosynthetic rate was 1.20 µmol O₂.h^-1.(mg protein)^-1.

Assuming no photoacclimation took place and this coral was lit by saturating light (metal halide or other) for just 4 hours per day, in that 4 hours it would generate 4.8 µmol O₂.(mg protein)^-1. However, during the 20 hours of darkness it would consume 14.0 µmol O₂.(mg protein)^-1. This would result in a net consumption of oxygen of 9.2 µmol O₂.(mg protein)^-1 per day. Oxygen concentration is directly proportional to energy use and so there would be a net loss of energy. i.e. it would not get enough energy to survive.

Photoacclimation would most likely take place which might put the coral into a better situation, but would it be good enough? Photoacclimation would involve better photosynthetic efficiency and a lower respiration rate. This is what is seen in the low light/deep water coral.

The low light/deep water coral had a respiration rate of -0.268 µmol O₂.h^-1.(mg protein)^-1 and a gross maximum photosynthetic rate of 1.19 µmol O₂.h^-1.(mg protein)^-1. This means the net maximum photosynthetic rate was 0.922 µmol O₂.h^-1.(mg protein)^-1.

If this coral was lit by saturating lighting for just 4 hours per day, in that 4 hours it would generate 3.688 µmol O₂..(mg protein)^-1. However, during the 20 hours of darkness it would consume 5.36 µmol O₂.(mg protein)^-1, a net daily loss of 1.672 µmol O₂.(mg protein)^-1. i.e. it also would not get enough energy to survive.

So, even the low light coral would not survive. The only way either coral could survive would be to have some other lighting either side of the 4 hours of saturating light. Note that the coral doesn't even need the 4 hours of saturating light if the other light is substantial.

Back to the original question... The corals would have 12 hours per day of darkness, 8 hours of actinics only and 4 hours of metal halide lighting. For the corals to survive, the actinic lights would have to produce enough light to provide the difference between the 4 hours of metal halide and 12 hours of darkness. If we use the example of the low light coral:

4 hours of MH: 3.688 µmol O₂.(mg protein)^-1
12 hours of darkness: -3.216 µmol O₂.(mg protein)^-1

The actinics would not need to force net oxygen production, but they would need some level of photosynthesis. As long as net photosynthesis produced at least -0.472 µmol O₂.(mg protein)^-1, the coral would survive. The actinic lighting should be able to achieve this.

If we look at the high light coral:

4 hours of MH: 4.8 µmol O₂.(mg protein)^-1
12 hours of darkness: -8.4 µmol O₂.(mg protein)^-1

The actinics would need to cause photosynthesis such that there was at least 3.6 µmol O₂.(mg protein)^-1 produced. It is unlikely that actinic lighting could drive this much photosynthesis.

The subject corals are going to be somewhere in between the low and high light examples here.

So... the answer here is the corals may survive but I'd say that may struggle. My recommendation would be to replace the actinics with daylight tubes. These will produce more PAR for the corals and not really add much heat.