Winterization of swimming pool

we have the pump on 2 x 1 hr a day all through the winter

Thanks for reply, but you don't say whether you have put winter chemical   in.

Yes of course and we have an automatic full cover (no gaps down the sides)

Thanks for your swift reply !

Hi can you please tell me what the winter chemical is ?

Sorry can't  remember, threw the can away yesterday, But I think it is made and supplied  by the big aqua people. Google winterize your pool. The instructions on the can are also in English. but it doesn't say about circulating the pool. 

I never circulate for 2 hours ! one hour a day in the swimming months.. Test done once a week and always a 100% I just use the tablets (2) made by the same people, also.once a week. I also have a water hoover, it cleans the sides as well as the bottom.again no problem .