Well, I would definitely check your chlorine/bromine levels. Run the filter. If nobody spilled/barfed/shat/ejaculated anything into it, that oughta do it.

If your spa is big enough, you might want to "shock" it -- that is, superchlorinate it to kill whatever might be mingling. But I'd check with your owner's manual to see if you can do that --most spas don't recommend that.

Finally, if you really had a lot of people in there and you're worried about it, replace the water. Stick a garden hose near a jet, hit the power and siphon the water out. Wipe the suface down, refill, re-chemical and you're ready to go! But there goes your Saturday! LOL

TT