balancing PAR intensity and duration

[Peter Houde]

DT:
125g, 6' wide, 2' vertical depth.

Lights:
4 Fluval Marine 3.0, 3ft 46W LEDs
pink 20%, cyan 55%, blue 100%, purple 55%, cold white 60%
until today: 5 hour sunrise, 2 1/2 hour daylight, 6 hour sunset, 10 1/2 hour sleep
new settings today: 4 hour sunrise, 4 1/2 hour daylight, 5 hour sunset, 10 1/2 hour sleep

PAR (Apogee AM-320, measured midday):
48-120 depending on depth, rock work, center transom and lid on one side

Corals:
slow or no growth: pocillipora (2 yrs), acropora (9 months), fox (9 months)
moderate to good growth: various montis, acan lord, duncan, torch, galaxia, favia, rhodactis, leptoseris (and hippopus clam)
overwhelming growth: various montis, discosoma

Observations:
I slowly started adding corals only 2 years ago after running FOWLR for decades, starting with what I thought were the easiest (some uncontrollable). I bought two small acro plugs most recently (9 mo ago), and placed them high in the DT (PAR 100-120) with strong flow. They bleached stone white within 2 days, one completely so I threw it out. The second bleached too for the most part, but there was still a little brown left to it so I lowered it in the DT (PAR 50 with much less flow) and it seems to have recovered ... somewhat. At least it appears to be alive, mostly brown but with small patches of green, and polyps rarely if ever visibly extended.
The pocillipora is a similar story. The polyps puckered up when I first introduced it 2 yrs ago mid-level in the DT, so I moved it to the bottom. The polyps stayed extended, but the coral has no color and it hasn't grown noticably in all the time I've had it. I moved it back to mid-level ony a couple of weeks ago and at least the polyps are staying extended.

Questions:
I think I'd like to increase PAR. I'd set the blue light higher if I could but it's already set to 100%. Everyone talks about PAR requirements for various corals, but what about duration? The PAR I've measured has been during the daylight setting, but are the corals getting enough if that's only for 4 1/2 hours? Should I shorten the ramp up and down settings of sunrise and sunset to lengthen the daylight setting? More to the point, what are the rules of thumb regarding overall daily PAR exposure? Apogee sells additional software (and gear?) to integrate this that I don't want to buy. But even if I had that information, then what should I be shooting for?

Caveats/Concessions:
I understand that circulation, nutrients, trace elements, etc all figure into coral health and growth rate. I also appreciate that some corals inherently grow faster than others. But no growth Pocillipora? Seriously? When others are doing so well? And I sure would like to see the acro succeed long term. I'm open to opinions and advice.

 

[rtparty]

120 PAR isn't enough for 99% of the acros out there. 200 is a bare minimum to shoot for for most SPS.

1 hour ramp up, 8 hour full, 1 hour ramp down.

Every coral in my tank was receiving 170+ PAR. Most acros were seeing 300-400 PAR.

 

[Hooz]

Speaking from my experience with Fluval 3.0 lights... Run the Blue, Cyan and Violet channels at 100%, then add white to preference or to make up extra PAR if you need it. The "Pink" channel I always just matched to the white channel. If you run your whites at 60%, run Pink at 60% also.

As for a schedule... If you want to run a longer duration, you can absolutely take advantage of longer ramps. That way your lights are "on" for viewing, but you're not frying anything. Just aim for a 4-5 hour flat "peak" in the middle of the day. So for a 14 total hour schedule, starting at 8:30am and ending at 10:30pm...

8:30am - Everything at 0
1:00pm - Everything at its max for the day
6:00pm - Everything still at its max
10:30pm - Everything off (0)

With the coral you have and the depth of your tank, I'd probably aim for 75-ish PAR on the sand bed, then see where everything else falls. Since you have to set all 4 lights individually, you'll have a bit of work dialing them in initially. I'd set them all in 10% increments, decreasing until you hit the PAR sweet spot. Then build your schedule off those numbers.

Set them at:

Pink - 60 ( 54, 49, 44, 39, 35, ... )
Cyan - 100 ( 90, 81, 73, 66, 60, ... )
Blue - 100 ( 90, 81, 73, 66, 60, ... )
Purple - 100 ( 90, 81, 73, 66, 60, ... )
Cool White - 60 ( 54, 49, 44, 39, 35, ... )

Check PAR levels, then decrease the settings for all 4 lights by 10% and check PAR again. Keep going at 10% intervals until you get 75-80 PAR on the sand. Make sense?

I just used the 60% whites as an example since that's where you have them now, but you can start them wherever you like based on the look you like. Just adjust your steps down accordingly. You really do need all the cyan/blue/purple the lights can give you, though.