Red fin (or red tail, which ever you mean) are NOT AT ALL peaceful. I have had them in the past, and I ended up having to rehome them due to constant aggression issues. Sharks of all kind, when kept singly, are territorial and get worse with age. The only time this gets better is when they are kept in groups, and, considering their large size, this isnt exactly easy to do.
If you really want a planted tank, I would take back the shark. they are just too much of a gamble, especially in a smaller tank. Now, dont get me wrong, I have a rainbow shark, which is supposed to be a more peaceful specie, in my 65 gallon and he is doing fine, no aggression at all.
I think it just really boils down to tank size and the persona of the particular fish you got. And I think that you got an angry little bugger. Also, 33 gallons seems a bit small to me.