First post of Outdoor grow. Pics+ Question

Hello, I have been a long time lurker of the site, often reading threads for fun and general information; learned lots.

It worries me that my first post should be about a plant problem, but it is what it is
My ladies have been in flowering for close to about 5-6 weeks; the LST'd girl is a week behind her sister. They have been maintained outdoors since sprouting and are in mix of MG Organic soil and MG seed starter soils with broken clay at the bottom for good drainage. The grow started in the beginning of May and obviously has been slow because of Geography. They are, however, free of bugs and have been getting as much attention as I can provide. Nute's are nothing more than an organic fish mix (Neptune's?) and standard MG plant food I found in the garage.

The first pics are of my Lst lady just before she shot into full flowering (the growth of hairs was small, but noticeable) Following these, are pictures taken today of the damage showing on the leaves. The sun has been dick'ish this week and hasn't shown, so she looks a little weepy, but sunshine is on the forecast for the upcoming days as well as nice temps.

Not sure, but I think it may be a Magnesium deficiency, if so, I have the Epsom Salts and water already waiting.
Cheers and Thanks!

hydro or soil

ive had a plant show very similar signs, turned out to be ph and a little over watering, check your PH and let us know

also mg soil can need a really good flush after a while, if ts in a pot, give it a really good flush....

Thanks for the replys!

First question: They have been grown in soil since day one.

Second question: I'm going to be going out today or tomorrow to get a PH test kit. Neglectful on my end to wait so long for this item, but better later than never. Will do. Oh yeah! I will be flushing tomorrow after I check the PH too.

Here are some more pics, the first two are of my other plant, who seems to be coming along fine, and the last is of the problem plant; just showing her flowering