If they were bought, what is the cultivar(variety) name? They may not be hardy here anyway. If they were wild, the hardiness is a toss up.

Iowa soils are usually not acidic, if that's what you are hoping. Sand may or may not be.

It's pretty fruitless to make soil acidic when they are in the ground. You need to amend to make the soil acidic from day one to day 1000. Dig an area at least 14 inches deep and as wide as you will need for the life of the bushes. Replace the soil with a mix of half native whatever soil it was and half sphagnum peat, and about 2 cups of ground sulfur or iron sulfate per bush. (It's okay to use up your Aluminum sulphate for this, but don't buy it again. Aluminum can build up and become toxic.) You could also mix a cup per bush of your preferred granular fertilizer if you want too. (Miracle-Gro is not granular, as it is mixed with water before it is applied.) Now you have by volume a larger amount of soil than you removed. Don't be afraid to mound it six inches above the surrounding soil surface. It will settle back in time. Don't forget to mulch your plants through the summer.

Virtually, your soil cannot become too acidic for blueberries. Future fertilizing can be done with acidic fertilizers like Ammonium sulfate, or the old Mir-acid (that is now in a green and yellow box called "Fertilizer for Azaleas, Camellias and Rhododendrons"). Fertilize not more than once a year, after blossom drop and up to a month after. Most fertilizers are already somewhat acidic, and you could use any good plant food, although those that claim to be acidic would be optimal.