I highly doubt its septoria... that usually starts on the older leaves ... what you DO have is a pH that is way too low for a soil grow so the plant isn't able to access any nutes it needs... which brings me to another point - you're not really feeding the poor thing. Seaweed alone isn't going to do much for her - she's starving for some decent NPK... if you want to grow organically, get yourself an organic nute line such as BioBizz ... but you've GOT to bring up that pH... it needs to be between 6.0 and 6.5...
Good luck....