Spray with epsom under the leaves @ 1 teaspoon per quart. Faster uptake of magnesium. Feed with epsom @ 1 tablespoon per gallon.
Get a ph tester, they're cheap. If your ph is 6,5 going in and 6 @ runoff then take the runoff value and deduct the difference from it (in this case it's 0,5) = 6-0,5=5,5ph.