To me, the 100 Euro per day to heat a small private pool (and only to 25 C) is just a money grab. It can't cost the hotel anywhere this amount of money to heat a little pool just a little bit. Also, I'm wondering how the guest can verify that the pool was actually heated if it's only to 25 C? Maybe the hotel says it takes several days, the guest pays, but with only a several day stay, the guest realizes no benefit from paying this ridiculous fee.