I also have psoriasis and I finally gave up and got rid of the hot tub.. I LOVED my hot tub, it was great and I used it 5 nights a week in the winter... My skin hated it and I suffered... I tried salt water, lower FC, higher FC, you name it... Kept it up for 5 years but had to go..
I am now going to build a sauna as that is great for blood pressure and skin and many other things...