I study chemistry, and to me, in its MSDS section 11 where the toxicity information is, it might be toxic if the product contained a large amount of Sodium tripolyphosphate.
Plus the health labeling is 2, normally it would just be zero, so if I were you, I probably won't feed the shrimps to my rays..........
Yeah, from what I read they use it to make low quality seafood look better, and if it's heavily sprayed it will soak up more water than natural. Also read that most seafood is sprayed with it. Not required to label it in the US
Do you have an asian market near you? I am an avid fisherman and catch over half of the food I feed my stock. If you choose to do so, you need to freeze at -5f for 48 hours+ to make sashimi grade and kill any parasites and bacteria.
Just some ideas. I can see you're really getting into this with your great pair. It might not be impacting you financially yet but man they can really eat you out of house and home in time! Especially if you feed pellets the costs really add up. Plus I'm a cheap bastard.