I don't use anything, I use a sand filter in mine.
I have a Hayward sand filter. It's a three. I use a a swimming pool size filter, so I have to change it every five years, so it's 300 pounds of sand.
It could fit into a traditional size jacuzzi or we have to have it specially fitted or what?
You'd have to have it specially fit because that filter is about this big and it keeps that water crystal clear. It won't stop algae, but I like the algae. I let algae grow in mine. I'll just scrape when it gets- the algae is like velvet.