By the looks of it from your pic ,the regal looks like a good size(3+ inches or so,if i had to guess)....In a 56 gallon he's probably stressed and that is causing the outbreak..TBH ,he will never be very comfortable in a 56 gallon ,,plus he's only going to double and triple in size....bottom line is your tank is too small to house a tang and will stress them out,causing ich to attack over and over