i think i know what type of yellow spots you mean.......the solution to your problem is to water them with plain water....the plants normally do not need ANY fert during the first 3-4 weeks from germination.....i had the same problem with you....in the same plant in different leaves two yellow spots appeared out of nowhere.....it was during the 3rd week of veg and nobody seemed to be able to answer to the question....i just watered them with plain water so as to stop the problem or even not to let it spread out to the rest of the leaves.....it appeared on one finger on a large fan leave.....up until now i haven't figured out what caused it...all i know is that with the use of plain water it did not spread to the rest of the leaves, the plant continued to grow normally as it should and the leave died slowly in its' turn......post any pics if you can