Photoperiod

[blennymower]

Can someone that has had experience with this tell me how long would 250watt 10Ks have to be running to start bleaching corals?

In a 75g (48'' long 20'' high) what's the longest allowable time given its lit by 250watt bulb 10Ks?

[muttley000]

You will have to state what corals, how close lamps are to the water, and how close corals are to the top of the water for someone to give you an answer.

[blennymower]

Mostly Light loving corals (SPS,LPS,Clams)

Some softies (leathers,zoas,etc)

anywhere from 3 to 6 inches from the water.

[greenbean36191]

Bleaching is dependent on lighting intensity, not photoperiod.

[blennymower]

Originally Posted by greenbean36191

Bleaching is dependent on lighting intensity, not photoperiod.

Ok, so then the guy didn't know what he was talking about. How close would an SPS have to be to bleach. I've seen corals 15'' or less from 400watt bulbs that have super colors.

[cdbias2]

Corals could show signs of bleaching almost immediately if they are not used to that strength of light.

[blennymower]

So let's say I buy frags from someone that has them under 400watt bulbs and then put them under 250watt bulbs, can they bleach?

[cdbias2]

Any new lighting can cause signs of distress which usually begins with some form of color loss.
Even an over due bulb change can cause it sometimes.

[blennymower]

Then how does one acclimate corals that were in higher light?

[Rouselb]

Originally Posted by blennymower

Can someone that has had experience with this tell me how long would 250watt 10Ks have to be running to start bleaching corals?

In a 75g (48'' long 20'' high) what's the longest allowable time given its lit by 250watt bulb 10Ks?

If you want to know how long you should run your light for, i would say 6 hrs min, and 12 max. I used to run mine for 12 thinking i would have more growth, but thats not the case. I actually get great growth at 8 hrs.

If you want to acclimate your corals to a new bulb or higher PAR then place the coral on a frag rack and slowly move it up over a month. Same for the other way, if you want to decrease the PAR a coral receives, you can place it on the rack and move it down until it starts to loose color.

A PAR meter is really helpful in determining when to change bulbs and where to place corals. I use mine all the time. I no longer just change bulbs every xx amount of time, i use a PAR meter to determine when i should. I also use it to know how much light i have on my frag rack, so i can place corals accordingly.

[Rouselb]

Originally Posted by blennymower

So let's say I buy frags from someone that has them under 400watt bulbs and then put them under 250watt bulbs, can they bleach?

Yes, it depends on what the K of the bulbs are, and where in the tank they are located. A PAR meter will help.

[Mattik]

I have a 250W 20K bulb, and I can't say that I ever have any problems with bleaching. Most of the corals are 6-10" below the surface and my photoperiod is 12 hours. I have increased that in anticipation of a bulb change. After I put the new bulb in, I will decrease light cycle to 8 hours, and adjust until I get the growth I desire.

Most of the corals I buy are from my LFS which has corals under 400W MH's, and I can't recall any of the corals I buy bleaching out.

I did get one from Live Aquaria that bleached some, but is still hangin in there....I don't know what lighting they have.

[blennymower]

Im in the process of getting new lights (MHs), the reason I'm asking this is before I got my T5s I had a coralife fixture (Coralife ballast and bulbs) and my sps frags SUFFERED under it. They colored up after I put them under T5s.

[Mattik]

Interesting. I have a coralife fixture and my corals seem to do fine.

I use XM MH (20K) and Coralife 50/50 PC's...

[2 TAZ]

I agree with a longer phot period dose not help, other then increasing you're eletcric bill. Coral growth peaks between 2 1/2 and 3 1/2 hours after the the lights turn on after 3 1/2 hours the corals stop utilizing the energy from the lights into growth. I have been using a 5 hour on and 7 hour off mh cycle and 6 hour on 6 hour off actin cycle for the past year. The theory is this scheldule should incourage more growth. I can't attest to an increase of growth due to other variable in my tank over the last year however I can say that all of the inhabitants, coral fish etc seem do be doing at least as good as a more traditional photo period. The big bennefit to me is that it significantly decreases my eletcric bill. Running the Mh for only 5 hours dose not increase the water temp as much requiring less chiller time. Also helps on the heater end to, less off time

[greenbean36191]

Then how does one acclimate corals that were in higher light?

When you're upgrading lighting, the two most common ways are to place a few layers of window screen over the tank and remove a layer every week or so or to just raise the lighting up a few inches.

When you just need to acclimate a new coral, you place it in lower light, high flow areas and then move it to higher lighting over the course of a few weeks.

Coral growth peaks between 2 1/2 and 3 1/2 hours after the the lights turn on after 3 1/2 hours the corals stop utilizing the energy from the lights into growth.

No. I have no idea why this is such a widespread belief in the hobby, but it's completely wrong.

The rate of photosynthesis is intensity dependent and has nothing to do with the length of the photoperiod except in a few special cases. Essentially as soon as the light reaches full intensity, the peak rate of photosynthesis is reached. It continues at the same rate for as long as that intensity is constant, be it 3 hours or 20 hours. The process doesn't bog down. The exception is when intensity is beyond saturation and is so strong that it actually causes damage to the photosynthetic machinery. In that case the rate of photosynthesis drops off as the damage accumulates throughout the day.

Calcification in corals is also driven by photosynthesis, so actual skeletal growth rates are highest when the lights are on. There is no indication that skeletogenesis bogs down with increasing photoperiod either, though this isn't as well studied.

[blennymower]

Originally Posted by greenbean36191

No. I have no idea why this is such a widespread belief in the hobby, but it's completely wrong.

The rate of photosynthesis is intensity dependent and has nothing to do with the length of the photoperiod except in a few special cases. Essentially as soon as the light reaches full intensity, the peak rate of photosynthesis is reached. It continues at the same rate for as long as that intensity is constant, be it 3 hours or 20 hours. The process doesn't bog down. The exception is when intensity is beyond saturation and is so strong that it actually causes damage to the photosynthetic machinery. In that case the rate of photosynthesis drops off as the damage accumulates throughout the day.

Calcification in corals is also driven by photosynthesis, so actual skeletal growth rates are highest when the lights are on. There is no indication that skeletogenesis bogs down with increasing photoperiod either, though this isn't as well studied.

I've read that eventually if you leave the photoperiod for too long zooxanthellae begins to be expelled.

If you never turn off your lights, this can't be good can it?

[2 TAZ]

I got my information from a study on coral growth published in the Journal of Experimental Marine Biology and Ecology. The study used a 4 hour on and 8 hours off cycle. The study found that motility, or growth, in the cells of Zooxanthellae algae occured only during the period of illumination and lasted 8 to 9 hours with a peak at 2.5 to 4 hours after lights on. You can find the article in the J of EMB and E volume 298 issue 1, 7 January 2004 pages 35 to 48.
For me the added benefit of less electricity was worth the change
there is also evidence of increased coral health using this cycle

[2 TAZ]

I believe there has been research done that suggest coral requires at least 5 or 6 hours of night time inbetween higher intensity lighted time.

[greenbean36191]

I've read that eventually if you leave the photoperiod for too long zooxanthellae begins to be expelled.

If you never turn off your lights, this can't be good can it?

Well constant lighting probably isn't a good thing. Corals build up reactive oxygen species during the day and their tissue becomes hyperoxic. Continuous lighting also seems to cause isolated zoox to multiply out of control and replicate their chromosomes too much. That would be bad news if it happened in the coral too. If your corals were continuously lit, you would probably get some problems, including bleaching, but that is a different situation than what occurs under normal photo-bleaching. There have been experiments that used 20 hr photoperiods without issue though. The caveat there is that the experiment only lasted 2 weeks IIRC. Extended photoperiods are certainly not something I would recommend.

The study found that motility, or growth, in the cells of Zooxanthellae algae occured only during the period of illumination and lasted 8 to 9 hours with a peak at 2.5 to 4 hours after lights on. You can find the article in the J of EMB and E volume 298 issue 1, 7 January 2004 pages 35 to 48.

That paper is about the motility patterns of free-living zooxanthellae. They swim best 2-3 hours after the light comes on. That doesn't say anything about their health or photosynthetic output. We do know from other studies that the drop in motility throughout the day is accompanied by a decrease in photosynthetic efficiency, but that the decrease is due to the cells preparing to divide. It's not anything that's inherent in photosynthesis. If the zoox aren't dividing, you don't get the decrease.

As it turns out, zoox in culture go through a daily cycle where they're in the growth phase for the first 2-5 hours of daylight, then around half of them enter a replication phase (and their photosynthetic efficiency drops). However, that's not the case in corals because the host regulates the cell cycle of their zoox. In corals, the vast majority of the zoox stay in the growth phase all day and only about 3-5% of them start to divide during a cell cycle. Under normal conditions you don't see the high division rates or drop in photosynthetic efficiency throughout the day that you see in isolated cultures. That's why both of those are used as indicators of stress.