Problems in second week of flower, any ideas? Yellowing with some brown spots and purple stems.

To me it looks like damage caused by excess nutrient salts in the soil/substrate. If you have not been watering to run off, this is most probable, especially combined with well water, which generally is a bit salty. Unfortunately, by the time the salts build up to cause damage, the problem in the soil is well advanced. This is why watering to run off is so important, as it flushes the soil and prevents the salts from building up. Giving lots of water now can cause more problems, as it can cause even more salts in your soil to be released and do even more damage. Drenching your soil until water runs out of the bottom of the pot is actually the correct way to water. Purple leaf stems are not a really big problem and can be ignored. At this stage I would give just plain water for a week or so, after removing as much of the fertilizer that is sitting on the top of the soil first. This way your plant will use up the trapped nutrient salts that are in the soil already. I would also be switching to a soluble fertilizer/nutrient, this way you can control what your plant gets, rather than feeding each and every time you water as occurs with the top dressing type of fertilizer you are now using. Worm castings are excellent and can not do any damage or harm, if they are pure and unadulterated. After this week-10 days has passed, I would resume with the fertilizer, but probably at half strength and as long as it does not cause further damage, continue at this strength until harvest. The problem with the top dressing type of fertilizer is that it feeds your plant each and every time you water. Also, after these 7-10 have passed, giving 2-3 litres of plain water would be about right. Ideally, you should aim for a water/water/feed/water/water/feed schedule, so that you are feeding every 7-10 days, with 2 irrigations of plain water between each feeding. This will be plenty enough food and the 2 irrigations with plain water will help keep your soil healthy and prevent any nutrient salts from building up. When you do water, water until water comes out the bottom of the pot, this is the only way to prevent salts from building up, otherwise, without run off, all the dissolved nutrient salts stay in the soil and build up to toxic levels. Hope this helps,............ Organoman.