We were in Caleta this Easter and it was very quiet, even though it was school holidays; although from what I've heard it's been a quiet summer season this year too, hopefully things may pick up next year. Apparently the all-inclusive hotels have been quite busy with everyone staying in the hotel for drinks etc, rather than spending money on going out in the evening.
Kids Clubs will definitely be running in the school holidays, but I'm not sure if they're still on during term-time, I know when we were up at the Caleta Dorada a couple of years ago, the teens club was only on during school holidays but the clubs for the younger ones were on all year round. I would check the small print in the brochure regarding kids clubs if I was you, or phone the tour operator Weather will be hot and sunny in the day (although you may get a bit of cloud and wind, but you can get this all year round in the Canaries...) It will be chilly in the evening in March, so take a jacket and long trousers. When we were there at Easter it was going dark around 8-8:30ish, but it got a bit chilly for the pool a while earlier than that.
Most hotels in the Canaries have de-salinated water in the pools. This is because the Canaries have no source of freshwater whatsoever (no lakes, rivers etc) so all water has to be taken from the sea. I have never thought it to be particularly "salty" though, it is very well de-salinated and with all the chlorine in the pool it doesn't have any worse effect than any other pool water. We stayed in a hotel in Crete last year which took their pool water directly from the sea, now that was salty!

i went to caleta in august and it was a lot quieter than any other place i,ve visited and we always travel in august.

March is a good month to go if you are staying in Corralejo, the carnival is on and it lasts for about 10 days, lots of locals come to stay and holidaymakers book holidays around it, it's normally early on in March - great fun!