Magnesium Deficiency ? How can I fix it ?

тут только 2 варианта. это либо недостаток магния либо не достаток Potassium. очень похожи их симптомы. но точно это не передоз.

Your pH should be at 6.2-6.3 for optimal growing according to your nutrients. Looks like you over fed something to me and it locked out the potassium. It’s not a magnesium deficiency. Magnesium deficiency starts at the bottom and will severely damage the leaves and work its way up as it’s a very mobile nutrient. I think you should just reduce the nutrients your using slightly and the plant should start eating normally again. The plants show mixed signs of potassium deficiency and nutrient burn so that’s why I am saying what I am.

Potassium deficiency and nitrogen over dose.

I think the problem is your pH here... get that down to 6.0-6.2 and both calcium and magnesium will be more available to the plants. I'd also suggest you buy some fresh calmag but only use it once a week as you don't want to overdose and get a toxicity of THOSE nutes! Your grow looks gorgeous and you've got quite a while yet to go so it would be a good investment... Good luck!