I have a 3 year old Bradford White Water Heater, Model M250T6DS5. I am getting white chunks of something in the faucet screens. I took it in for analysis at our laboratory and it is not calcium. I have drained the water tank twice and flushed it out. Bradford White representative said it does not sound like dip tube pieces since it turns to powder when rubbed between fingers. Some of the larger pieces (about 1/8"-1/4") are about 1/16" thick and barely curved as if having been stuck to something round. Any ideas?