I'm not sure about saltwater but I tried it in freshwater when I found out my school of 50+ tetras were sick with ich. I had shrimp and snails in the tank that I wanted to preserve, so I went and bought this medication.
The first few doses, my tank was fine. However, as days went on and more dosing had to be done, it turned out, the medication wasn't as invert-safe as it claimed to be.
From my experience, this is what I took from it:
1. Takes a long time for this medication to cure ich compared to copper based products.
2. Not 100% invert-safe.
3. Ever since I dosed enough medication in the tank that ended up killing my shrimp and snails, I could never add any more inverts in there as they would all die within a day. Even after water changes! It must have been absorbed in the substrate.
4. I'm probably not going to use this product again.
This was done in a FRESHWATER tank though. But hopefully that helps. Inverts in both fresh and saltwater are similar in which what would kill them, medication-wise.