Dry Amendment x Strawberry Banana Fast Buds

There's where in lines your problem. Different soil at the bottom. Your plant is going through massive ph imbalances. As Mouse says. 150ppm is far to low at this stage. And she seems to be taken up too much water (and that ph is all over the place as there's hardly any buffers from nutrients in your pot. The rust spots I've had with nute clashes and the plant drinks more water than anything..

Not calcium deficiency. 6.8 - 7.0 should not cause any problems for the plant. Anything you do will take 10--14 days to show in the leaves, not 2 days. Calcium deficiency will be dots, not large blotches.

PH a bit high. I'd try and lower it down to aorund 6.2. I also think they look a bit hungry as well 150ppm is a bit low. you also mention it gets 0.6EC. can prob bump that up to 1.0EC even 1.2 just look for signs of bruning and enrure you ahve some runoff to prevent buildup.

Could be easily be a calcium deficiency, as well as an out-of-balance pH. You seemed to have fed plants heavily also. Other than that, it can just be a bad plant. It can happen at times. You can expect that even when working with clones. It looks like temps and humidity are quite high too, given you're in 5th week of flowering.

Good luck.