Mag Def? please help, keeps getting worse and worse

I am currently 4 weeks into flower under a 400watt hps in a grow tent growing using Roots Organics Soiless mix. There is adequate airflow and a moderate temperature. I use the General Organics line mixed with Roots Organics with no problems with other strains. My 3 Sweet Thai plants seem to be suffering from the same thing which i think is magnesium deficiency. I keep raising the CaMG+. With other strains 7.5ml/G was enough and leaves were always very green and healthy. I have gone up to about 12.5ml/G, but i have noticed the leaves keep yellowing and dying off and getting worse. At first i thought it was just a Nitrogen deficiency, so i increased the biothrive grow from 15ml/G to 30/ml G. Anyone have any ideas how to remedy this. The PH is fine its around 6.1. Also last week i was worried about lock out so i leeched the medium. Any help would be really appriciated. i scared the plants wont make it till harvest.
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You're locking out the P & K with too much Mg. Also, over wet mediums cause Mg to lockout, plus others.

Did you check the Ph/Ec of the flush?

Perhaps lower the Ph to 5.8. ur run-off may have been high 6.0's.

I would just water a few times and change the PH a little.

Most Sativa plants are sensitive to nutes, any idea what ur ppm is? What water are u using?

Oh they will make it to harvest. There is plenty of green on them plants left. In the last couple weeks of flower the leaves start to yellow and fall off anyways. I would flush to reset your soil and start feeding according to your nutrients feeding schedule for what week you are on and stick to that. Adding all that stuff during flower not knowing exactly what the issue is has caused your soil to become very salty and toxic....nutrient lockout is a bitch....Less is better

Its now rootbound and starting to yellow, look at the rootball.