Seems like it might have a load of bleach in it!
http://slimygrimy.com/product/slimy-grimy-granular/
Hit the Before and After tab at the top of the page and there is a video!
Looks like oxalic acid to me. Just make up your own boat cleaners and save some money. I keep muratic acid, oxalic acid, bleach, and laundry detergent and make up various cleaners to clean the boat. That’s all I used to restore my 37 year old whaler.
“Wailord”
1979 17’ Montauk
90 Johnson
Wilderness Ride 115