Let's understand the "mantra" of "never" changing your sand: It means that unless your sand is actually fouled, as yours was, replacement is not a necessary part of sand filter maintenance, so don't waste money on new sand every year or even every 5 years. But if it is broke (as yours was) then, by all means, fix it.
Carl, this is exactly what I wanted to get across with this additional point: It took me a while to figure out that the sand might actually be the problem due to inexperience AND reading posts here that say the sand does not need to be changed. Many of these posts do not include an "unless" qualifier, so I'm hoping that the next person searching for help will run across this post and be aware of it just in case.