Lighting.

[Rama89]

So I went to a chain pet shop locally here to get some snails and crabs to boost up my CUC. I notice their coral tank is lit only with the blue spectrum.

My question, is this sustainable or only in a retail situation? I have by blues on only as I am having an issue with dinos. I will start bringing the whites up at some point but jeesh, even when they are on for day just an hour the dinos go crazy.

Everything else in the tank seems fine with just the blues. As a matter of fact. When I have the whites on, even set at the min, no. 1. The GSP don't fully open.

Dave

 

[ISpeakForTheSeas]

Some people run pure blue lighting all the time; some people run white light - both work fine (though pure white may cause some browning of corals - not in an unhealthy way, just in a coloration way - and pure blue hides a lot of the colors of fish and other critters in the tank); which is best depends on the individual corals (literally the individual specimens, not just their species).


Anyway, for a more detailed rundown on white vs. blue light (this is mentioned in the quote below, but I typically suggest a full-spectrum (i.e. white) light that has a lot of blue and only a bit of red (too much red is not good for corals, but a little red may or may not be better than having no red):

Yeah, I've posted on it before - for the simplified version, both algae and coral will grow fine under either white or blue light; some people believe algae does better under white light, but that may or may not be the case.

However, certain corals do better under white light while others do better under blue light; I usually suggest a full-spectrum (i.e. white) light that leans heavy on the blue and light in the red (too much red is not good for corals, but a little red may or may not be good).

Similarly, some kinds of light may be important for some species of fish/invert, but may not be strictly speaking necessary.

Anyway, for the long versions (posts 59 & 63 in this top link):
https://www.reef2reef.com/threads/white-lighting-as-it-pertains-to-algae.975639/page-3#post-11224375

The study below tested Acropora variabilis and Porites lutea harvested from 2-6 m deep at maintained 6 m deep; they compared dark (no light), full-spectrum (the control), and blue light settings at 200 μmol and 400 μmol (they tested full-spectrum at 800 μmol as well, but 400 μmol was the highest they could get the blue); they used a metal halide light with polycarbonate filters to control what spectrum the corals were being exposed to - the corals grew (calcified) fastest under the blue light, but there was more photosynthesis under the full-spectrum (white) light:

"The light to dark calcification ratios of A. variabilis under 400 μmol photons m−2 s−1 of control and blue light were 8.4 and 10.5, respectively; while lower ratios were observed in P. lutea (3.4 and 4.5). In both cases, calcification under blue light exceeds even these of the control"

https://www.frontiersin.org/articles/10.3389/fmars.2015.00122/full
So, under controlled PAR with metal halides, these shallow water corals grew faster under blue light than white, but but photosynthesis decreased drastically under blue light when compared to white.

To contrast with that, though, another study (using three different species of Acropora - A. tenuis, A. muricata, and A. intermedia at 100 μmol and 200 μmol [low numbers, I know] with LED's) compared different spectrums (the first link below) and found that the inclusion of some red light drastically increased the growth rate (the second link below; the green/yellow spectrum made a little bit of difference, but they didn't add much of it in with any of the three spectrums used; it may have made a bigger difference at higher intensities):
https://www.researchgate.net/figure...study-A-PBR-400nm-purple-430nm_fig1_367478086https://www.researchgate.net/figure...erent-light-spectra-Values-are_fig6_367478086The actual study:
https://www.researchgate.net/public..._physiological_adaptation_of_Acroporid_corals
Another contrasting study - Stylophora pistillata from shallow (3 m) and deep (40 m) waters; the shallow specimens showed the highest photosynthesis rates under full-spectrum lighting, but the deepwater specimens showed the highest photosynthesis rates under blue lighting (sadly, they didn't measure growth rates, and the study only took place between March and April, so it was rather short, and results may have changed if the study had been longer).
https://journals.biologists.com/jeb...-spectral-quality-of-light-is-a-key-driver-of
So, does blue light grow Acropora or other SPS faster than full-spectrum (white) light? It depends on the coral (both species and individual specimen), the location and depth/temperature the coral is from, what light the corals are photo-acclimated to (a shallow water coral growing under blue light in a hobbyist tank for 5 years is likely going to be acclimated to blue light despite its origins), year-round weather conditions (storms and such play a big role in determining what light is reaching the water), the clade of zooxanthellae they're using, etc.

Does the kind of light used (metal halide vs t5 vs LED, etc.) make a difference, or is it all in the spectrum, intensity, and photoperiod? I don't think we'll be able to answer this unless someone is able to make LED's with the exact same spectrum as those other types of lighting, but I'd guess any differences would be minimal.

So, lots of different things go into the growth, and again, fast growth doesn't necessarily equate to excellent health/coloration (it might, but it also might not). Does each coral species have it's own optimal spectrum for growth/health/color? Probably, but I doubt it would perfectly match a different species own optimal spectrum, so I don't know that it would much matter in our tanks - instead, we'd need to find the optimal spectrum for a broad range of corals, which may not be optimal for any particular coral we keep:

"Zooxanthellate corals display contrasting photoacclimation responses, coral cover, colony morphologies and genetic richness along depth gradients33,49,50,51,52,53,54, which collectively suggest that coral species occupy different light niches."
https://www.nature.com/articles/s41598-022-25094-5
Personally, I'd expect to see similar (not the same, but similar) growth rates from a lot of corals under both blue and full-spectrum lights; some will likely do better under one than the other, but determining which is a lot of effort.

For that reason, like I've said before, at this point in time (barring a major, undeniable scientific breakthrough with our knowledge of corals and light), I would personally only suggest running the windex blue tanks if you really want to see the coral fluorescence pop (as mentioned by others, though, the colors may be best in the long run if you run different spectrums than just blue throughout the day). Like many others have mentioned in various forms by this point, I'd personally run a full-spectrum (white) light that leans somewhat more toward the blue side of things. Is that the "best" spectrum? Maybe, maybe not, but it seems like a good, safe place to start from.

TLDR; white and blue light both work for coral and for algae; what's best for one coral or algae may not be the best for another (even of the same species).