Leaves drying out?

Hi,

Im new to cultivating, but none of the guides I have read so far mention anything about this. The lower leaves on my plants, are becoming brittle & dry, turning yellowish/brown and falling off, but its still making nice new leaves. They are about 2-3 weeks old.

Its getting 24hrs light all day and just enough water, whats the problem?

Thanks

Sounds like fertilizer burn or a pH problem.
What are you feeding, how many nodes do the plants have, what is the soil, and do you know the pH of the soil runoff?

Havent fed them anything yet, I thought they didnt need food added until after the first month. I have to check the pH, that could be it.