Browning curling leaves

I've been having the same issue since the word go, every single plant I grow hits roughly week 5 in flower and starts wilting away to nothing. I am using X nutrients full strength, 1 tsp cal/mag and ph'd to 6.3 - 6.4. Each round of plants I have tried less nutes, more nutes, cal/mag, double checking PH and still I get this. Everything is under an air cooled 1000w HPS and in happy frog soil.

Any thoughts or suggestions are welcomed.

Looks like a phosphorus deficiency/lockout to me. Too much Cal?

well first off i you ph is the issue locking out other key elements next time try to maintain 6.8 - 7.0 ph you will see a major difference

Flush with proper pH. Looks like P. That soil has organic nutes so full strength isn't needed. Xnutrient folk are cool ask 'em about your tomatoes.

it still looks like nute burn to me...alot of sativas are very picky..also make sure you have plenty airflow

What should proper PH be? The Xnutrients schedule says maintain 5.5 - 6.5, which I have been following religiously.

Even with 1/2 strength nutes they all start doing this.

Today is feeding time, so I will Ph to 6.7-6.8 and see how they like it.