You NEED to be using RO water. Not RO mixed with tap to save a few bucks. Any of the gallon sidtilled water you buy from walmart will be under 10 ppm. Then you can actually add the right amount of nutrients. I still think 625 without knowing what's in your water is pretty damn hight for a plant that size. If you've got a lot of calcium in your water, and you're adding calmag on top of it with a mag lockout due to calcium you see how it can get screwy. You need to be starting with RO/Distilled water. It's like 5 bucks for 5 gallons. You don't want the spring drinking water shit because they add minerals and salts to it for taste which is bad for your plant.
Looks like your plants are getting bad quick. I'd get some epsom salt(magnesium sulfate), mix a teaspoon in a gallon of water and use it as a foliar spray. I keep some on hand, but I've learned that the best way to treat calmag problems is to not let them happen in the first place. The problem won't always show up right away. In fact, Magnesium problems generally take a while to show up(sometimes not until flower) but when they do they can be more of a bitch to correct. That will buy you some time to figure this out.
You've also got some burnt tips which definitely looks to be nute burn...
I would Flush for a day(run pure PH'd RO water and nothing else), refill with store bought RO water, Cal-Mag and proper ratio's of nutrients and wouldn't go any higher than 300 ppm for a day or two and see if anything gets worse. That will give them plenty enough nutes to live and heal without making shit worse until you figure out what happened. Don't expect your plants to just bounce back and start growing right away either, they've taken the beat pretty good and it might take a few days. It's very possible that they have just been overfed at some point, and they are experiencing lockout. If that's the case then theres nothing you can add to it to fix it. You've just got to flush, and try to draw out the nutrients from the plant that are causing lockout before the plant will be able to uptake all the shit they need in the right quantity and balance.
Also, try not to disproportionately feed the plants calmag. Keep the ratios right in line with the rest of your nutrients.
I really hope you get it sorted quick Man.
Peace.
Tav.