Those parameters aren't perfect, but nothing that would cause mushrooms to bleach/disintegrate. What do you have in your tank for livestock? How long has it been set up? Ever used copper - or had the tank ever previously been set up for FW
It could be a possible predator - have you examined them closely for odd-looking snails, nudibranches, etc? .
Even lighting (depending on the exact 'shroom, and where they came from) is an iffy topic. I have a tons of 'shrooms
, button polyps, and star polyps in our refugium, under a Home Depot shop light - they've been there for months now, and look perfectly fine.
What about calcium levels?
Why are you adding Iodine? Have you confirmed low readings via a test kit? Any other additives?