what is causing this leaf problem? help please

6 weeks old from seed
In mapito
Moved from floro's to 600w few days ago to speed up growth of these mother plants
26-27oC
ph 5.5-5.6
humidity around 50%
ec 0.3 (low because start to nute burn the other week was 0.
Good air out, air in not fitted up at the moment - could this contribute?

Pics shows only worst leaves, other leaves have none of slight amount of same problem. A couple curl up, others just look like something has been spilt on them.

help!?

I have had leaves that look like that when they get too much light too quickly, for example when switching to bigger lights too quickly. You mentioned that you had just switched from floros to a 600 watt, so I'm thinking that might be what's causing this for you as well. I would recommend moving the lights a bit further away to give the plant time to adjust to the 600 watt light.

It kind-of looks like a light (heat) burn. the leaves look dry, crisp. id say move the light away some more, maybe 24in. from tops, atleast!!

thanks guys I've moved the lights away