I have been having problems with sediment (looks like large pieces of sand and tiny rocks in varying colors of brown and black) accumulating in my faucet aerators and shower heads. I installed a whole house filter at the water main thinking that the water coming into the house was simply "dirty". Then I cleaned all the aerators in the house, and even decided to clean out the lines for my washing machine. That's when I realized the problem is with my hot water only, because the cold line to the washer was super clean but the hot water line was full of the sediment. It is so bad at this point that I am cleaning out aerators on a weekly basis, otherwise there is no pressure or hot water at the faucet or shower head. The washing machine keeps giving me an error code becaue the hot line is full again and no hot water is getting to it. I have an electric tankless water heater and I thought that there wasn't supposed to be any sediment with a tankless heater. My home is less than five years old and I live in Tucson, Arizona. The water has been tested and the hardness is less than 10. Anyone have any idea what is causing this problem?