We have a 2-story house, with basement, on a well and with a water softner. About 2 months ago we noticed a signifigant drop in water pressure whenever we flushed the toilet, ran clothes washer or any 2 things at once. Both hot and cold water are affected. On the advice of my brother-in-law we replaced the pressure tank. This was no help. However, my husband did buy a larger tank than the original. Could this be the problem or something else? The problem is getting worse and sometimes there is no water upstairs when the washer is filling. Can we fix this ourselves or do we need a plumber?