As soon as you get yourself an Ec meter the problem can be solved via the run off. I highly doubt it’s ph going in and more likely an Ec issue. Either the plants need more feed to increase the levels of calcium going into the plant or require flushing with the addition of less feed after, due to a salt build up altering the ph in the rootzone.
The addition of a cal mag solution is a myth imo and the chances of a calcium deficiency is not likely given your base nutrients contain the required amounts.
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