From the photo, I can see only one clear area you describe. If it is a condition affecting many fins, then this is more serious than if it was just the single fin I can see.
The fish is being irritated by something; or something is off that is preventing the fish from handling the irritant. That 'something' or 'somethings' are a very large grouping of possibles. It could be something a bit exotic like a coral or invertebrate stings, or (more likely) a water quality and/or nutrient issue. The water quality and nutrient issue quite often goes hand in hand.
I'd review all water parameters. Check that you've performed your maintenance. Remove any collected detritus or dirt in the system. Perform a careful large water exchange. You're looking to reduce any excuse for bacteria to be present. Be sure your skimmer is working and any organic exporting is up to snuff.
You can help the fish by providing it the best nutrition and foods. You may want to review its diet and the feeding frequency, since it should rebound from such things you are seeing, on its own, if there are minor water quality issues.
The condition can worsen. If you still think/see multiple fins in this condition, it is best to treat the fish for a bacterial infection. Investigate possible injury sources, try some of the above, add immune boosters to it diet (Immune Boosters), and monitor the fish closely.
--OR--
If you do see the condition widespread on the fish, then the fish should be moved to a hospital tank and given a treatment with an antibiotic, such as Maracyn Two for Saltwater Fish. While the fish is being treated, find out what is happening in the aquarium that may lead to increased bacteria population and improve the diet the fish is getting.
what other type fish do you have i had a couple of pajama cardinals that werent doing so good and it turne dout my trigger was eating them, so dont rule out other fish
while I was checking out my tank I noticed my tank was hovering around 83degrees. Turns out my heatrer was being silly so I pulled it out. Next morning the temp was back to the 79ish range and the spots were gone Thanks for the help everyone.