A rotating spray ball uses the pressure of the cleaning liquid to spin its head, so the jets move around and hit the tank walls with more force. This makes it great for getting rid of sticky or baked‑on residues. It also uses less water and chemicals than a fixed one, and it cleans faster. But it has moving parts, so you need to maintain it from time to time. It costs more upfront, and if the liquid has debris in it, the small nozzles or bearings can get clogged or damaged easily.
A fixed spray ball, on the other hand, has no moving parts at all. It's just a ball with holes in it. That makes it very reliable and almost maintenance‑free. It's cheap and works even at low pressure. However, it mainly just rinses the surface rather than scrubbing it with strong jets, so it struggles with tough dirt. You also need a lot more water and longer cleaning cycles to cover everything, and on complex tanks it can leave blind spots that don't get cleaned properly.