Repotting Helvola?

I have a Yellow Canary Helvola in my 50 gallon pond, and it usually
covers the surface in the summer, and the blossoms are beautiful. I
have been repotting it every year, but I have not done so this year
because it actually had several leaves all winter long. My questions
is should I re-pot it now, or do I even need to re-pot it at all? By
re-potting I mean the the place where I bought it sold my some clay
and said it should be done every year. And I placed river rock on the
top of the pot, should I do that? I read somewhere that that isn't a
good idea, I don't know why.

Thanks,
Gary