wilting?

hi, does anyone have the slightest idea why both my k2 plants wilt towards the end of the day at around 7pm, the lights go off at 11pm. there both in all mix bio bizz, and one has been fed 1ml/litre of bio grow. ive just bought a moisture metre and im only having to water every 7-8 days. both plants are about 10 inches and are under a 400 watt hps. btw ive just bought this light, does this need a ballast? also, will it be cooler than my hps? thanks if anyone could help me out.

http://www.growell.co.uk/p/0909/Brig...one_Light.html

its the 4 tube 1

They look self contained to me.

ok, thanks zandor, any idea why my plants wud wilt from about 7pm onwards. its bloody weird and i cant figure it out. on some of the leaves they also seem to curl under at the tips, but other than that look pretty healthy. thanks once again zandor youve helped me out so many times, cheers

:)When I lived in CA. mine use to wilt at the end of the day, I would give them some water. And in a few hours they looked very healthy again. This may not be your situation, but maybe try it one day.

Dude... three years old... poster and plants long gone. Please avoid bumping old threads.