Cameron

A few days ago I noticed one or two small discoloured spots, which got worse by the minute, until there was quite alot of dry crispy spots and tips. Luckily it stopped increasing/spreading and is just fixed, at the moment. Keep in mind that it is only a small indoor grow, more as a hobby, and my LED grow light is about 20W. I've also been giving her RO water. She showed pistils a day before the spots appeared. So, I would like to know if there are any suggestions as to why the spots are appearing?