Kessil

Feeding zooxanthellae and light par requirements

Some Acropora can do well in relatively lower light. Red Planet is one of them, but it tends to stay green in lower light, pink/red in higher light.

You can have relatively low PAR, but still provide high amounts of PUR (especially when using a lot of violet/blue light. Unfortunately, reading PUR requires expensive equipment and most hobbyists only have access to a PAR meter.
 
I have been quite baffled by this same observation, when I last used the PAR meter I saw max readings of 120 at the sand bed & 450 3-4" from the surface and I thought wow I don't have enough light on there. I cranked up my LEDs and corals started bleaching, dialed the lights down and started increasing again but very slowly and still a few SPS started bleaching.

I gave up & dialed down my lights to where the corals respond best and that's literally about 100 max at sand bed & <400 at the top. All the colors are great, growth is as at it's fastest now since I started this tank. To top things off when I bring browning corals from tanks with more light than I have they quickly color up & start growing in my tank.
25% of all my LEDs are UV/Violet. For some odd reason this has not stopped me from wanting to upgrade lighting :D
 
As you can see, PAR readings are really only a rough guide. A 400 PAR reading in your tank could potentially give very different results in someone else's tank due to type of lighting, how much PUR the lights are putting out, water clarity, duration of lighting, ramp-up/ramp-down schedule, etc.

Upgrading lighting is always tempting, but if you have a system that is giving you great results I'd think carefully about it. A change of lighting puts a lot of stress on corals, especially Acros that are often pushed to upper lighting and low nutrition limits to produce bright pigmentation.
 
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