whats wrong with my plants

[cittauk]

I had to put my 3 plants back under a florescent light while I figured a way to disperse some of the heat caused by the sodium lamp as this was making the top leaves go dry and crispy, curling up at the edges.
While back under the florescent for a couple of weeks some of the lower leaves on one of my plants began to get yellow spots (see pics)
None of the other plants seem affected and all new growth looks healthy, but I would still like to know what these spots are.
Also I would be grateful for any tips on keeping my grow room cooler as even when the lamp is over three foot above the plants the temperature is around 88f.
I have installed a small extractor fan in the ceiling but this seems to make little difference. I can't knock a hole in the outside wall for an intake fan, but I do have the window open slightly behind sealed curtains.
The lamp I am using is a 400 watt hps with a seperate ballast.
I would appreciate any advice this is my first attempt at growing my own.
citta

[cittauk]

Seems my post has been viewed quite a few times but no one has replied please someone out there must have the answer. Have managed to get the temperature right but the yellowing of the leaves is still occuring seems to only affect the lower leaves. has anyone got the answer?

[OVERGROWER]

Looks like you have the early signs of mites or white flys..
Had a plant get mites started just like that and before long the whole plant was compleatly infested..
I have used "seven dust" insecticide with good results.
good luck with your babys

[TK-Zao]

Doesn't look like mites to me but check the underside of the leafs for white dots just to make sure.

I'm pretty sure what you have is a ph problem though.