Most likely that is an Iron(Fe) deficiency. Most likely. Although the burnt, up-curling leaves with inter-veinal discoloration That your leaves have is what concerns me as this does point to possible Mg problems. If the tips of your older fan leaves turn yellow and curl upwards and then exhibit "chlorosis discoloration" that IS indicative of Mg deficiency. This can be caused by feeding too much Potassium(K) to your plants. if this is the case uptake of Magnesium, Manganese, Zinc and Iron can be aggravated. It can also severely affect the plants ability to use calcium which is essential.
use one or both of these products as part of the regular feeding schedule and that should stop.
http://www.sea-of-green.com/big-bloom.html
http://www.sea-of-green.com/earth-juice-microblast.html
Caution: the microblast goes a long way and must be diluted to about 1/4th dosage to feed everytime. for that reason I use 1/2 strength doses of the Fox Farm Big Bloom for regular feeding and then will give two feedings with light doses of microblast. each has some stuff the other doesn't, that's the only reason i switch but it works for me.
Also i have been taught that it is best to underfeed and under water your plants a bit than to over do ANYTHING. Overdoing anything will cause you far worse problems that those little spots.