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You can use CalMag, however it won't solve your problem.
It's impossible to tell without more information from you, but it looks to me as if you are pushing them too hard with nutes, causing what seems to be a minor overfert problem.
Again, impossible to say without knowing more about your salt concentration in the mix, etc, but that is my suspicion with next to little information. Dial it back and flush with water, see if you see an improvement. Then start again with a lighter EC.