A pool guy is typically compensated for their services based on the number of hours they work, the level of difficulty of the job, and the client's budget. There is no set amount to tip a pool guy for Christmas, but a common gesture would be to give a small monetary gift or a holiday card with a personal note expressing gratitude for their services throughout the year. Alternatively, you could also give a gift card or offer a holiday bonus if you have a particularly positive relationship with the pool guy.