"I does calcium iodine and strontium/molydenum once per week"
From your rundown of parameters it sounds to me like you arent testing for the stuff that you are adding to the tank. If you dont have a strontium/molydenum test and KNEW you had a defiency, Why would you dose it? The same goes for anything you would dose to the tank. If you dont have a test kit and know there is something lacking, dont dose it. My guess is something is out of wack parameter wise within the aquarium. I would move the gsp down to the bottom of the tank, do some water changing and get some test kits for calcium, alkalinity, magnesium, iodine and anything else you might want to dose.
In my experience with 2 different varities of GSP is that they dont like full intense light and they dont appreciate super heavy flow. They do great for me in high light and moderate flow.