Api general cure and seachem focus mixed together with pellets or freeze dried food. The focus binds the general cure to the food
I think this is a much better cure for parasites, as Prazipro does not seem to be as effective.
That being said, how did you (the OP) come to the conclusion it has parasites? Joker asked if you've seen it poop. You said you haven't. The fact that you have not seen it poop does not mean it has parasites. You could have just missed it.
White stringy poop that has trouble coming out indicates parasites, a lack of poop does not.
The fact that it has a sunken belly and is eating would be an indication of parasites, except that it is eating TDO, which is a carnivorous food. I know you said it is also eating seaweed, but the question is, is it enough? My experience has been that these blennies do not do well (i.e. live long) unless your tank has a lot of algae to graze on naturally. They don't seem to eat enough of what they are actually fed. Despite their small size, usually this means they do better in large tanks.
Unless I saw white stringy poop, I would still think it is starving. And the method of soaking in General Cure and Focus is not something I am sure will work on Seaweed.
If the fish is eating pellets, try getting an herbivore pellet like Formula Two. And I would feed the Formula Two before the TDO and spaced well apart. That way the blenny eats first and is hopefully consuming less (or no) TDO.
Edit: I would soak the Formula Two as described by Chris if, and only if, you confirm it is parasites and not starvation.