Answer: Most vegetables will grow within a fairly wide pH range of say between 5.5 and 7.5 but 6.5 is just about ideal. Having said that, and knowing the pH tends to drift over time, good vegetable soil is usually somewhere between 6.0 and 7.0. Melons do best between 6.0 and 6.8.
Melon sweetness can be diluted by too much water applied too close to harvest that particular year; since your melons were large this is what I suspect may have happened. However, if your melons are never sweet, it is possibly due to a shortage of boron and magnesium. To remedy this, use a mixture of 3.5 tablespoons of Epsom salts plus 1.5 tablespoons of a 20 percent boron material (look for this in the laundry section of the supermarket) per gallon of water. Measure carefully because you do not want to use too much boron! Apply this mixture when the vines begin to run and again when the fruit is about two inches across.
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