Corals reaction vs photoperiod

[anakjoh]

I use a 150W 14000K MH suspended ~ 1 ft above my 2ft 100 lt tank. I noticed that almost at the end of the normal 6 hrs photoperiod (6 pm to 12 am), some corals ie heliofungia (looks like anemone but was told it's not), star polyps and even the jewel sometimes, will "close up". All other corals are still open basking in the strong light.

Sad to say that temp is usually 28C but sometimes nearly 30C.

I've noticed this phenomena for some time but never bothered to ask before. Can someone offer any explanation/advice?

[Tanzy]

Maybe the water temperature has risen too high after baking for a while under the lights. I've seen the corals you have mentioned opening fine under stronger lights for longer periods of time without problems. I'll suspect temperature.

[Achilles Tang]

Agreed.

High temperatures are a stressor for corals. Don't be surprised by a bleaching episode soon.

Why don't you install a fan in the meantime before you get a chiller?

[anakjoh]

Thanks for the prompt replies!

I'm using a fan but it's at the sump rather than the main tank. I suspect temp's the prob but just didn't want to admit it coz trying to avoid buying a chiller. I will pay special attention to the temp.

This pre-CNY season is particularly hot but windy.