Not sure what you mean by 'scarlet skunk' but it probably depends on your budget

Fire shrimp are more expensive and tend to hide a little more. The reg. cleaner shrimp (white with red stripe down the back) are cheaper and pretty much do the same job. Both of these will do well in pairs - not sure you need more than two. You'll have to make sure you don't have predators in the tank - these guys make a tasty, expensive snack for some fish.
BTW, I've had my fire shrimp for almost 3 years and I believe it's because I target feed it chunks of thawed, frozen food every day (read: equal bio-load to fish).
HTH