Although a moisture or nutrient imbalance might affect fruit quality, you say the tree is lovely, which suggests that it is not lacking anything. If the tree is otherwise healthy, your tree may be an accident. Most peach trees are grafted onto a rootstock, meaning that the top part of the tree is a different variety from the roots. Sometimes the graft fails and the entire tree grows from the rootstock. Rootstock types often don't have good fruit (instead, they tend to be hardier, shorter, or more disease-resistant-traits they give to the top part of the plant). Unfortunately, you won't know this until the tree bears its low-quality fruit. I suggest three options. Take the fruit to the nursery to show the error and ask for a replacement tree. If someone at the nursery knows how to graft, or knows someone who does, ask to have a good variety, or even more than one, grafted onto the tree. That way you won't have to wait for a new tree, and you could grow a tree with several varieties of peaches.If you are adventurous, join a group such as North American Fruit Explorers and find a member nearby who can teach you to graft. Then you can graft other varieties onto your tree.