What are your thoughts?

I took this pic a few days ago. I notice the yellowing in the leaves and I am wondering why. They are about 3-4 weeks into flower. They are in a 4x8x6.5 with 2 thousand watt HPS with co2 in 2 gallon buckets. I use GH floranova, liquid karma, cal mag, budswel liquid, pure blend bloom organic, kool bloom liquid and dry, and superthrive.

I'm using tap water with a start ppm of 200-300. I got the cheap meter. I'm wondering if the problem is the hard water? I guess it could be burn from to much nutes but I'm not sure. Any advice is welcome and thanks in advance.

A lot of strains do this around week 4 so i like hit them veg nutes at week 4 then straight back to flowering nutes, they wont reveg it just stops the rapid yellowing.

^^^^^^^^ Thats what you should do this time. Next time, use veg nutes for the first 2 weeks of flower and that wont happen.

you guys are awesome. Thanks