Hi, Extranjera ! Yes. the Black Sea area used to be a famous resort to Russians. Nowdays, they more tend to south, like Egypt, India, Maldives, Thailand. I'm Russian. I don't think we have to break the natural rules. I have a gorgeous estate in Sochi. I do not need Maldives in winter. Make sure, the fact, like staying in Russia in winter real bolsters your immunity !
The Black sea in my area (Big Sochi) never freezes and I swam there on 2-d of Jan one year.
As for pond system, I wish you would visit us sometimes ! My neighbor is a big expert and gives some advice. He feeds the pond with the fresh brook water, then it stays there for some time. Then, I believe, once per month, he lets the water go filtered naturaly through the ground. That makes available servicing of the pond, plants, etc.