I also think the leader on this thread got it wrong.....the idea is not to increase photosynthesis at all. If anything you can see that corals have no trouble getting enough light to photosynthesize, and that's where the danger is. Photosynthesis is destructive. So they make a point of protecting themselves in lots of ways. If we go around hacking the system to boost photosynthesis, they are going to be under more stress and suffer additional damage compared to what is normal.
I am with you on not increasing photosynthesis. There is even a line of thought that Manganese is used to inhibit photosynthesis.
Zooxanthellae algae are brown algae that use photosynthesis to grow/reproduce. This is a symbiotic relationship with the coral. NOAA states that " Most importantly, zooxanthellae supply the coral with glucose, glycerol, and amino acids, which are the products of photosynthesis. The coral uses these products to make proteins, fats, and carbohydrates, and produce calcium carbonate".
If we interfere with this process to color up a brown acro, we are reducing the Zooanthellae by either starving the algae [unl system] or interfereing with photosynthesis.
But if the zooanthellae are not present to provide for the coral then the coral must get it directly from the tank. This is why we have high fish populations, then feed our fish very heavy, dose coral foods, use aminos etc. etc.
With all this in mind, and reduced zooanthellae, I see the topic of low/high par like this:
Low Par/ High nutrients= LPS Heaven. But for acros , it usually means tan or brown color with growth because of the nutrients.
Low Par/ Low nutrients= Better balance with some color and allows for the use of higher alk to boost growth.
Higher Par/ Low nutrients= Bleached starved corals. You are stepping on the accelerator but the motor is getting no fuel. The coral has no algae for protection from the light and no energy to form it's own pigments. Throw in higher alk and you speed the process up even faster. The acros appear pale and bland at best and show little to no growth.
Higher Par/ Some nutrients= The corals are forced to form their own pigments and have the needed energy/food to do so and to sustain growth. Photosynthesis is greatly reduced but it doesn't matter. The coral is not depending on the algae for it's food and provision source. I like to run a little bit lower alk [NSW] to slow down the process and to be a little more under control. This cause a little slower growth, but is a safe trade off for control and color.
The last group I stay away from;
High Par, High Nutrients, High Alk. I see this as a high energy metabolism system. A runaway freight train on the razor's edge. The guys who can pull this off, I salute you. You are SPS Gods. High color and fast growth.
), but ultimately PAR is still a more useful value. There has been an aversion to LUX in the hobby historically due to it being the measure of light both in and outside the spectrum of usefulness to your corals/photosynthetic critters (and therefore potentially misleading since it doesn't just measure what is useful)...but IMO this fear is often a bit exaggerated since the fixtures we use at this point are all designed to be focused on delivering light within the PAR spectrum (at least primarily).
