strange plant behaviour!

Hi guys,
Right i appologise for the lack of pictures but bear with me.
My plants have been looking great bar a couple of random yellow leaves at the bottoms every now and again but after the last night cycle they had all become droopy and sad looking.two of the five had all of the leaves facing the floor! I have now put them onto 12/12 and watered again to see what will happen and after only 10hours they have all purked back to theoir normal happy selves,or seemingly anyway?! So just a couple of questions for you all, firstly has to be why?they are all in 11 litre pots with bat mix soil,under a 400w hps. Secondly, on average how much should i be watering them? Litres wise? I think i may have been too carefull with my water and not given them enough.they get around a quarter of a litre per day. Last (for now) is how long does bat mix soil hold its nutes for?i was under the impression of around 6weeks?if so that would make sense as they have been in that soil for 6weeks exactly now.
Thanks for any help

When your plants droop like that they need water fast. Yea, you should give them more.
Its hard to say exactly how much more but they shouldnt droop like that between waterings. The closer the light is to the soil the faster it dries, the bigger the plant the more water it needs. One thing thats worked for me is to get one watered good and pick it up. Feel the weight and get an idea of how much it weighs watered. Then I pick up the pot to tell when she needs water. 11 liter pots are a bit big to do that though. Double the frequency of waterings to start, they will pick up.

Good luck.

they will need more water, just water them until you begin to get runoff out the bottom of the pot
and water when the top of the soil begins to dry out.

thank you very much guys ill see how dry the soil seems when the lights come back today.really hope it is just a water problem.ill give them a decent amount and maybe move the light up a little,its around 6" above them at the moment
Thanks again