na dann....
If I remember correctly, from some of the tanks that I've seen using all
T5 (mostly in Germany), people were going with about 12 hours of light. I would start from there and see how your corals do. It should be sufficient. I can speak at least from mine (albeit not the amount that you're wanting to do), 12 hours doesn't seem to harm them at all and I think the fish don't mind having a bit of light!
einen schönen Tag noch!
