Popeye.

Looking to get some help and advice here please on Popeye and how to treat.

Basically a few weeks ago one of my Piranha developed popeye pretty much overnight. I just put it down to injury and would monitor over the next few days. Thankfully within 2-3 days the eye was looking good and the swelling had gone. All good and what a relief.
Now, yesterday I noticed one of the others had developed popeye pretty much (again) overnight. All was fine the day before. I'd started to ask myself if it was just an injury picked up again purely by the way they will and do dart around the tank at times. This time though the swelling is a little more severe. This is what's making me think little more than injury (hope I'm wrong). Other than this the fish is in good health and so are the others. All water params are good with regular/weekly large water changes. I'm happy to wait and see if it clears on it's own over the next fews days, but I need some help on how to treat if I have to take action. I've read many times that Maracyn 2 is the best treatment to use, but the downside there is that it's not available in the UK and to order from the states would not be here for at least a week. On the plus side though, I've also read that Epsom salt can be an effective treatment whcih I already have. I also have bottles of Pimafix and Melafix at hand.

Please could anyone advise? Would really be very much appreciated. Thank you in advance!!!