7.5~ pH - Is Citric Acid a crazy way of bringing it down? It seems like mixed in with water and such it would be fine. If M-Gro is acidic it will resolve.

Best way to lower the pH without harmful chems use apple cider vinegar two tablespoons per gallon will drop pH from 7.5 to 5.8-6.0 garenteed use in every gallon

Just get Ph up and Ph down. They're a few bucks each. It's really not worth messing around with over a few bucks, long-term. I used ACV once last grow and it was fine but over long-term it's just a few bucks and it's months of work. Get Ph up and Ph down.

Citric acid is a decent way, though not ideal (it's a weak acid), very good component though (as it's central to plant metabolism and can aid nutrient uptake. Ascorbic acid could be added to that, along with say, sugars or acidic nutrient components (maybe like tartaric acid, which is potassium stuff).