Glad it worked out for you Dudley. I've had this issue from time to time and dealt with this the same way. I feed Tetra Bits to my young fish but generally crush it up a bit between my fingers before feeding though I haven't had this issue with it, mostly it's been with fish over consuming lower quality flake food.
Some strains, like Blue Diamonds, seem more prone to get this type of extreme constipation and I've lost one or two along the way before being turned onto Epsom salts as a treatment. When it's especially bad I will also use an internal antibiotic like Kanamycin Sulfate in conjunction with Epsom salts to prevent a possible secondary infection.
My one Blue Diamond is extremely healthy at this point but I did have to treat for internal infection at one time. Even when she's in good shape she seems to excrete in large, wide, circular volume in a way that is very different from all my other Discus. It does seem that there's something a little different about the plumbing in this strain than some of the other strains.