HELP What is This

It's a Nitrogen deficiency. Your ppm is 1400. IT SHOULD BE 850. You should be feeding BIOGROW: 2ML/L BIOBLOOM: 1ML/L ALGMIC: 2ML/L Nthing else at this stage. Please follow the bibizz feeding schedule online.

I had the same problem. I solved reducing the feeding so, lowering the EC. Try to reach a PH of 6.2/6.3. Raise the light or decrease his potency and wait 2/3 days. The plant will recover easily. Be careful now, youre in flowering and there is no space for mistakes. A good tips could be to do a little flush with ph water only, but do it only if you'are sure that the soil will dry in not more than 4 days.

growdiaries.com/diaries/191415-barney-039-s-farm-glookies-grow-journal-by-jsanchezz 6.3PH and 2.3EC your EC is to high. get it down. max 1.8 Ph is on point. light might be a bit to close at 17" but double check that. that high of a ec is likely to cause more issues that mimic deficiencies when in reality its locking it out but it is there. Good Luck!

Red stems, light colored foliage and the brown spots lead me to think Phosphorous or Magnesium Deficiencies. I went through your diary and couldn't find what Ph you are feeding at so I'd start there. Make sure your Ph is in the optimal range for your medium.