Discuss with me your PAR range throughout your tank. It seems (based on some numbers you provided) you are getting 150 on bottom, up to 400 or so at top of the tank.
Hi. Here is a PAR map of my tank as it was a couple of years ago I think...forgot to be honest...tank does NOT look like that now. This was the 2nd reset of this tank.
Previous to the current incarnation of the setup, I was running the LED's at 700mA. Now running at 350mA and PAR has decreased a little around the edges (T5's unchanged),
with most of the drop in PAR around the middle/under the LEDs...this has balanced the PAR spread across the whole of the tank with little or no hotspot) At 700mA I felt it was a little too much PAR in the centre area...see the numbers on the PAR map.
Some of those numbers are just too high IMO (particularly since I am using a combo of T5 (which bathes most parts of a coral and Blue LED's which are high in PUR and very directional). Whilst most corals were very colourful, a small number were a bit pale for my taste.
Here is a sample of photos when this SAME system was at its peak (the previous year) with the PAR numbers as those in that PAR MAP:
It really does sadden me to see how good my tank was and that I lost it all...and had nothing but problems the past few years...
To continue the discussion; With the LED's at 350mA, most of the corals receive 220 to 250PAR. I have one rock which reaches fairly high in the water volume, and it is here where the PAR is around 400 at peak. You have to remember that my tank is only 18inches high, the water line is almost 2 inches away from the top due to being rimless...then subtract 24mm from the bottom because the tank has 2 x 12mm bases...which makes the water height somewhere around 15.5inches, so the PAR drop isnt much.
The corners of my tank right at the bottom is around 150 even with the LED's at 350mA. At the centre of the tank on the bottom its about 190-220.
The weakest area is where I have planted the Red Planet; I wanted to retain the green colouration in the Red Planet...at higher PAR it loses the green.
So to sum up; most of my corals get around the 220-250PAR, the Red Planet, Branching Cyphastrea (which is not an SPS), and a few other deepwaters/smooth skinned Acros get the lower end of the PAR level.
A selected few like Milli/Prostrata type get the higher end at 250 to just under 400.
(Note also that the Apogee meter under reads by about 5-10% depending on the diode wavelength).
I know that fixture is a monster with PAR, so how high do you have it above the tank? Do you find the best coloration at these PAR levels? How is growth effected when PAR is 300 vs 600?
My ATI Sunpower unit sits 8inches above the waterline. I would say that colouration is fine at these PAR levels. I wouldnt be able to really tell you if the 300vs600 which would be better because back when I used 250w Metal Halides with T5 supplements, I didnt have access to a PAR. At 600 PAR a lot of SPS will reach photoinhibition and would be trying their best to stay alive, so growth will likely get slower as you reach photoinhibition levels. Going by this same setup, when the PAR was much higher, I would say some colours were perhaps a little more intense (eg greens), but overall, colours are just as good when I had slightly higher PAR, with some corals like I said maybe a little pale.
This fits in nicely with explanation in literature. - See:
1. Chart showing PAR requirements of certain corals:
2. Table 1 right at the bottom of this article: - Table 1. Compensation, Saturation and Photoinhibition Points of various reef animals (which includes a few more SPS species not in above chart:
http://www.advancedaquarist.com/2007/3/aafeature1
3. See also this article which goes into explaining how certain colours with appear more intensified under higher PAR:
http://www.advancedaquarist.com/2009/1/aafeature1
The articles has charts such as this one which shows that over 400 PAR the intensity of certain colours diminish:
4. Aside from Literature, here is a post by another RC member with LOTS of reefkeeping experience, completely agreeing with me in respect of PAR requirements from a practical point of view:
http://www.reefcentral.com/forums/showpost.php?p=22072763&postcount=183
You seem to be one of the few trying to minimize PAR to your corals to some extent....as I've noticed some other tanks pushing 600-900 where some of the top acros are....however, they do appear a little pale to me...
Like the reefkeeper I linked immediately above, a lot of us old timers will say 250 is plenty...It doesnt need to be 250...it could be 300 etc, but its the sort of figure that in my experience is a good baseline, and if you know you are hitting around 250-300 on most SPS and they are still brown; then you need to look elsewhere like your water quality etc.
So with regards to PAR levels for SPS, yes, in my experience one can have very good colour in most SPS with about 250 PAR.
It also seems PAR can be pushed differently depending on lighting source.
Leds seem to do best from 150-300
T5s somewhat similar but are a little more forgiving 150-450
MH seem to be most forgiving, 150-600....i rarely see people bleach coral with MH....
That is along the lines of my experience as well. Particularly with LED's...I think they are so directional and most of the light from LED's hit the upper surface of the coral...whereas with T5 or MH the coral is hit with light from a far greater range of angles ie very diffuse light with T5 and with MH due to the large reflectors etc.
I would like to hear your thoughts about your particular PAR and your beliefs it has on coral color.
Well, you have my thoughts and a lot of it is backed up literature too.
Get the baseline PAR and concentrate on your water quality, keeping your paramters stable, keeping the hands out the tank and things like pests.
You wouldnt believe it, but my first SPS tank was a nano tank lit with 3 x 18watt T8's. This was more than about 12 or 13 years ago...back then nano tanks werent taken as seriously as the larger tanks...and many people did say that you couldnt keep acropora healthy and coloured up in nano tanks due to swings and low light levels. Well I did. And I had good colour too. But I did have the SPS corals 3 inches under the waterline with the lights only 2 inches above the water. But it worked and I had nice colour in my SPS.
Light is only one factor in SPS corals. As long as you got the baseline: ie around 250 for most, less for others like Monti Caps etc then your lights are fine. Where extra PAR will most likely help is when the tank is in a eutrophic stage, extra PAR will cause the coral to expel at least some of the Zooxanthellae.
Water quality and
food has SO much more to do with SPS colour than light IMO...because it is very easy to hit most SPS with decent PAR.
In respect of SPS growth, with decent light levels and stable parameters and Alk, Ca and Mg at suitable levels one should get decent growth rates.
