Help!!! I think my plant has some type of plant deasease!!!!

Hi im using a 400w hps cool tube thats hooked up to a filter and an inline can which is blowing towards the outside of my house. Im also using a circulating fan and i have never had heat issues. 2 out of my 4 plants started getting brown spots on the leave wich always originate on the middle top part of the leaves and eventually spreads.some buds are loosing color and going into a lighter green, towards the buds and begining of the leaves. I red that this could be a form of plant desease, and every day i notice a little more, and a little more. What do you guys think???? should i continue this grow or just harvest what i have now???? THE PICS DONT SHOW THE BROWNING

What's your pH? What's the pH of the water you're using? medium you're growing in?

well if it isnt a disease the buds usually stay alive and well while the leaves self destruct soooo, in my experience hold off on harvest unless u see reall bud damage not just lighter buds, also some of those leaves are so dark that in comparrison buds are yellow but, hold off on harvest is my advice unless u find out it is a disease of somekind that will destroy everything but youll figure it out, what strains u got there?

what's your container size? are you running nutes in accordance with feeding schedule or something custom? what're your temps? what's your pH? media? feed/water schedule? more info, broski. provide as much as you can.