Hi Susan,
what are you trying to achieve?
Most water clarity issues are easily solved with good quality Granulate Activated Carbon (GAC).
I never heard of Seachem Clairty, but there is plenty of negative reviews in freshwater forums...
I am fan of Seachem products because they specify their composition, which most brands don't, but unfortunatelly I couldn't find it for Clarity. So, I can't comment from the chemestry point of view.
Having that said, I would stay away from it and explore a product with proven record in marine tanks.
There are other floculants available on the market. I have experience with KZ Coral Snow and more recently with its DIY version (CaCO3) and while it didn't harm anything, I haven't noticed any significant improvement in water clarity nor in reducing particulates in the water column.
On the other hand, people swear by its ability to remove cyano bacteria.