Legal Question in Real Estate Law in California

I'd say the starting point is to determine whether the damage was caused by the tenants or by the passage of time. Pools need periodic maintenance and repair even when not abused, and if this is the situation, then you should go ahead and repair it at your own expense, or in the alternative, rent the property without a useable pool. If you are pretty sure that the tenants are responsible for the damage, then it becomes a question of deducting the repair cost from their security deposit and/or taking them to small claims court (if they won't settle voluntarily). Also, you need to discuss the overall issue with your rental management company, preferably face-to-face rather than by phone or e-mail exchanges. Let them know you expect their pro-active assistance in getting to the bottom of this problem and figuring out who is responsible. After all, this is one of the reasons you pay them a management fee -- the management company probably isn't liable itself, but it is being paid to handle or to assist in handling such problems.