somewhat minor problem

hello everyone, i am Atomsk. 18 year young male residing in socal

This is my first grow that of witch is somewhat experimental so i can asses what my plants need before starting a full crop.
i am running a 400w mh/hps and using FF ocean forest soil and technafloras recipe for success nute kit.

i am now about 6 days into flower with two random female strains, i vegged them for only about 3-4 weeks because i was unsure of gender and in the time have only fed them up to 1/2 strength veg nutes but i plan to work up to full strength veg and then start to use the flower formula. i am now noticing a light green starting from the tip of the lower leaves and working its way in. looks to me like a calcium def but im not too sure and its only very visible on one plant and very very faintly on the lower shaded fan leaves of the other.
i use tap water and do not currently own a ph meter but seeing as this might be the problem i am going to pick one up along with some ph+ and ph- or some dolomite lime later today.

i would very much appreciate any help in identifying my problem!

here are some pics of the deficiency from the bottom fan leaves witch are mostly affected to the higher leaves witch are the least affected

After you test the ph, and if the ph is good then most likely a nute deficiency (calcium maybe). Although, u should add more info such as grow room temp, humidity, etc.

Do you use CalMag?

Yea I thought it might be. An I have yet to get a tempature gauge. But the area stays very ventilated and cool with the fan running. About mid 70's maybe a tad lower. I'll update soon with the water ph. Just need some calibration solution >.> haha

No I don't. Will it help if it is cal deficient?