We purchased a foreclosed house last year. At the time of purchase in August (in Sacramento CA), the tree had 30 or so large beautiful oranges the were sweet, thin-skinned, and virtually seedless. The property had had no irrigation or maintenance for about 2 years. The tree is some type of grafted tree. The base of the trunk is about 10 inches diameter. I came in and lovingly cleaned up around the tree, faithfully fertilized every 4 weeks during spring and summer, used a soaker hose through spring and summer to water (trying to be careful not to get its feet too wet). The tree is planted at what is basically a huge berm so there is a lot of drainage. We got thousands of beautiful blossums and now have hundreds of small, almost tangerine sized fruit that have lots of seeds and are on the sour side. The rinds are still thin, but much tougher than before - the previous fruit rind was also thin but peeled so beautifully. The color on the fruit is also not nearly as pretty, kind of a yellow cast to the orange. What do you think has happened or is happening?