Although tipping is not a requirement, it is always most welcome. When and how much is totally up to you.

If the treatment was outstanding and it leaves you satisfied, by all means tip anthing from 10% up. You should, however, not feel obliged to tip - you should still receive a good service even if you don't.

If you're a regular and you make use the same facility quite often, it would be nice to leave a tip regularly. When in doubt phone the spa manager and aks what would be suitable. You can leave the tip at the reception desk when you pay your bill, just specify who it's for.