Natural pool on the roof terrace, Ibiza

What do you do if you build swimming ponds but live in an apartment on the third floor yourself? Build your own small natural pool on the roof terrace!
Admittedly, a somewhat daring undertaking given the climatic conditions on Ibiza. The dimensions of a queen-size bed with a water depth of 50-60 cm in full sunlight in the middle of the Mediterranean ... is already at the limit. But the small natural pool has proven itself over the years! The separately installed filter does not win a beauty award, but does its job very well.
Year of construction 2013, total water volume 2.4 m3, of which 1 m3 in the filter