When my knees see the light of day, the sun shines for more than four hours continuously, and the temperature rises to 20 C and above; it's time to start thinking about swimming.
Usually we leave opening the pool until June 1st, but we begin to think about it in mid-May (i.e. now), and the very first thing to do is empty most of the water from atop the hibernation sheet of black plastic.
A few years ago I bought a special pump to deal with the water, but it has always proved to be a problem. You don't just chuck it in the water, and flick a switch. It has to be carefully positioned with its ridiculous 'floater' up in the air.
To achieve all this requires the combined brains of Heath Robinson, Grandpa Bungie Potts, and Jules Verne.
In winter 2019/20 I shall work on a floating island, into which the pump will sit. It will float around the pool, keeping its depth constant, and pumping away like a trooper. I'm already working on a prototype.
For the moment I do the above.