If seaweed is affecting Paradise Beach is will also be affecting all of the other beach clubs - they are lined up along the same side of the island.
If you don't care about the inflatable toys and HUGE pool at Paradise Beach, then Nachi might be a better fit for you. Limited occupancy (under 130 guests per day), good food/drinks/service.
Only Paradise and Sanchos will offer a PAYG option, and then only if they have space available. If you do not need a sandy beach look at the Money Bar - no admission fee, PAYG, good snorkeling from the shore (you enter the water via steps), and lots of lounge chairs and room for sunning/relaxing.