Rust Spots. Calcium Def?

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.

Necrotic fan leaves won't heal, but you can likely prevent it from spreading into the buds' sugar leaves. The whole plant looks hungry as well but that may be the lighting. So your cal problem looks even worse than it might be. You could feed in with a minimum 20% runoff at a PH of 5.2-5.5 to attempt to average out the high PH at the roots..measure your runoff until its 5.9ish. Butvi, I am thinking there an imbalance and lockout. It reads like you're using a super soil like ffof or ffhf. Usually measuring on the low end low PH out of the bag. These store bought super soils usually are geared towards the veg stage and then become imbalanced through early flowering. I found them to be good for about 1.5 weeks per gallon in veg and only 1 week of flower before deficiencies would arise. Looking exactly like yours. Lower end necrosis moving up the plant. Often, low PH, likely you described but with calmagic added and then using a lot of PH up through flower, the PH up can build up in the soil and get hi as well.. especially with cloth pots that don't water evenly IMO.. Flushing periodically became regular practice, changing the imbalanced soil to an inert soil before flower started. Then, adding microbes helped for a short bit. I had to flush the media until it was very inert. Like 100-250ppm from 1000s and then immediately provide flowering nutrition for the remaining weeks. Each strain can have completely different feeding requirements. Some hungrier than others. With super soils in flower, one plant may thrive a certain soil and the one right beside needing something completely different and showing stress amd deficiencies or worse, in excess. You could also guarantee to correct the PH with good RO water flush 3X the volume of your container. Then, immediately add a balanced properly PHed flower nutrients solution. This prevents the chance of any imbalance. Get some color back into the whole plant as well. Then let the media completely dry out between waterings. I used to like cloth bags, but after a few grows, they became PIA to get even waterings and more difficult to flush. If you decide to flush and feed, i wrap the bags with shrink wrap or alike so the water pushes down. Wet and come back 20 min later to finish flushing it out. Get a good shop vac or bucket vac to make cleanup easi. or drag it to the laundry tub to do it. Throw some bleach down the drain later.. Happy growing..