hey - most probably this is the first report of an 945 altimeter failure (as far as i know :D ); you could give the watch a warm batha nd wash it with a mild soap, but most probably it's defect and will be replaced by garmin
Usually this problem occours with pool treated with havy chemistry
Not sure that's true. I've been a pretty heavy user of Garmin watches in pools for many years. I've yet to have issues with the altimeter. I think there are a number of people hypothesising that the altimeter issue is related to pool chemicals but that hypothesis is far from proven. If the problem does not resolve after cleaning AOM, and anyone else with this problem, should contact Garmin Support.