Q.Clementine Fruit Very Bitter
Our clementine mandarine tree puts out a ton of fruit, but the fruit is so bitter that it cannot be eaten. We’ve only been on the property about 3 years. The tree is approximately 20 years old. We pruned it when we first moved and since then it produces well, but the fruit is still bitter. There are other orange trees on the property (navel and valencias) that are producing just fine. Any tips?

This article has some basic information on clementines: http://web.extension.illinois.edu/state/newsdetail.cfm?NewsID=8553
There are many varieties sold under the name "clementine," yours may just not be as sweet as you expected. Also, there's always a possibility that the root stock is what is growing and producing - those are usually less pleasant tasting. I've seen various suggestions for sweetening citrus fruit, such as less water, extra phosphorous, or 1 cup epsom salt every 6 weeks. You might give some of these a try - nothing to lose.