dribbzzyanswered grow question 4 years ago It looks like a phosphorus deficency and also you may have a magnesium deficency too, try ph your water to 6.2 to 6.5 you should get better results also phosphorus is an element that takes the longest to break down in fertilizers and use as food for your plant in all plant based nutrients hence why a few growers use phosphorus 2 to 4 weeks before flowering to store up in the leaves and get an instant supply when the plants change growth hormones from vegeative to flowering.