Holes within the tail are usually a sign of rot (but you'd see it primarily on the edges), decorations, or high ammonia.
Otherwise I'd go with what I suggested earlier..
Originally Posted by Myates
Fin rot you will see blackening edges with crusty/flaking pieces as well as shredding.
If it looks like a sideways U, he could be fin biting, a sideways V it could be a snag from a decoration. You said he was fine yesterday so I'm inclined to say it's either biting or decorations. Remove any plastic plants that are sharp and pointy. Some of those "bushy" plants have little points that are notorious for tearing up fins.
Stress Coat or Stress relief will help with fin regrowth. Either use that as the conditioner, or put in a few drops along with your regular conditioner.
Keep up on your water changes (is your tank filtered? If so, you don't want to do 100% water changes, if not, continue with what you are doing). You can add in an extra 25% water change per week until he starts to heal up to prevent rot from forming.
Stop using spring water.. it lacks the minerals and nutrients that they can only get through tap water.
I wouldn't use AQ salt until you are for certain it is rot with the coloring and crusting, or you get a picture up and it is confirmed by others you have it. Salt has potential to slow down the fin growth as well as harm internally.
If you are using spring water, are you also using water conditioner on a normal basis? You always have to use conditioner, and again.. spring water is a no-no. I think your previous loss (which I am sorry to hear) may of had something to do with the water and chemistry rather then a few small holes in the fins... it usually takes a lot and a long time before they pass due to fin rot.