leaves yellow on sides

I think the EC tips and possible overfeeding is also good candidates (B4RNS and ORGANOMAN comments) so I decided to flush all plants at least two times. I don't have EC meter currently and it's bit out of my range right now but I think flushing cannot hurt (maybe slow down the bud growth but that's risk i'm willing to take - better than lose whole yield)

I thhink you are right on the potassium deficiency. Do you use filtered water? If so u have to add more of all the minerals and salts. Keeping your PH in check should help. Good luck!

Banana leaves, tips burned. Check the EC of the drain. The EC of the soil might be a bit too high. Keep it below 1100ppm (2.1ms)

Looks more like nitrogen overload rather than any sort of deficiency to me. Once leaves are damaged like this, they will stay damaged and will not return to normal health. By the time your plant shoes symptoms of deficiencies or excesses, the situation is well advanced already and one irrigation of pHed water will not do anything. To remedy the situation will usually take around 7-14 days and the results will be shown in the new growth, not by the older leaves. This condition was not caused by having your substrate at 7.0, which is just about perfect for soil grown plants anyway. Since you don't have any info about nutrients or feeding schedules in your diary, this makes it difficult to give anything more than a general advice as an answer to your question. Try to wait until the top inch or two of the soil is dry before watering again, as a too wet substrate can cause some of the symptoms showing on some of the leaves too. Having a water/water/feed/water/water/feed routine will also help prevent problems from over feeding and watering to run off also, will help prevent fertilizer salts building up to toxic levels in your plants soil mix. Hope this helps,........ Organoman.