Ive been running two emp 400s on a 90 for a little over a year now. They have been thoroughly cleaned monthly, water tubes for bio wheels, disassembled and cleaned impellers etc. Lately Ive noticed they arent putting out as well as they used to, which leads me to my question...What do you guys think the problem is here? Its not the filter cartridges and baskets slowing it down either as they are not clogged, Do I need to order some new impellers you think? Thanks guys.