yeah it looks like you may be over feeding...i would say it was chemical burn but theres not any burn but on one or to leaves in the pic, or maybe you took the pic when it first started ,anyway id check your soil iand flush the nutrients out and you should lower the p.h of your water to 6.5......also from the look of how dark youre leaves are you may be over feeding.....its better to feed well once or twice every week then letting the soil dry and doing it agin (tip) my friends like to stick there finger in the soil and if the first three inches is dry then its time to water......that keeps distibuting all through your pot over feeding will make them all bunch at the bottem of the pot..