Calcium Deficiency?

Your leaves look to me as though they have been burnt by getting the leaves wet and then sitting under your lights for a while, or even damage from hitting the side of the pot when your fan is blowing. Calcium is only needed in very small amounts at this age/size and if as you say your soil is well prepared, there should be enough calcium in it already. One other thing, as a personal suggestion, I would recommend that next grow, fill your pots up to the top. The lower branches will get more light while they are forming and your plants will have more room to grow roots. After a while, the soil usually settles down and compacts a bit, so your plants will have even less room to grow than they do now. With full pots and extra/more soil, your plants will also have more access to nutrients, requiring less frequent feeding with fertilizers. Also, even though you are using the "air" pots, your plants can still get root bound, therefore the more soil that is in the pots, the less likely that is going to occur as soon. Remember, healthy roots = happy plants! Hope this helps.... Organoman.

Looks like more of a ph spot to me. New leaves look ok. Wait before you give anything. Watch new growth. Make sure ph is proper. Cheers