my Kera sativas are unwell

[Lhenry]

My 2 previously healthy sativas turned sickly with small brown/rust-like circles appearing on leaves, then yellowish, then brown then dead. there are no holes, just small distinguishable circles, like a pox..?
This was just noticeable about 2 weeks previous. Just a note: I have 2 other plants in the tent with them, and they are thriving. No signs of spots or brown anything, it should also be mentioned that they all received the same exact treatments and TLC as all my plants. I am perplexed, I have been pouring through pictures and can not find my pox ridden plant. I will try and send photos. this is my first grow using seeds. My pictures are on my phone, and I have no clue how to access, but I'll figure out.

[Blowdout2269]

Hello Lhenry! Yes, pictures would help. So would more information about the grow(i.e. type of medium, environment, nutrients, lighting, ect.)
But, just going off of your description...most spotting on leaves is a result of incorrect pH. Do you check your pH regularly?