Answer: If you used potting soil in your container, it should have a slightly acidic pH because of the peat moss. You won't need to add anything to keep the flowers blue, especially if you use Miracle-Gro (or Miracid) as a fertilizer. If the flowers are not as blue as you'd hoped, you can add aluminum sulfate the following winter (before the flower buds develop).
As far as diluting the fertilizer, use half of the suggested amount (I use 1 Tbsp in a two-gallon watering can) and thoroughly water the plant with however much water/fertilizer solution you need. If the container is still thirsty, mix up another solution and water some more. I try to keep the fertilizer solution off the leaves because it leaves a white residue when it dries. If you want to sprinkle it on the leaves (it's called a foliar application of fertilizer), you can lightly rinse it off the leaves when you've finished feeding.
Hope this clarifies things for you! Happy gardening!
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