You are loosing alot of efficiency due to scale build up from lack of
maintenance, flushing. I had a tank replaced , we opend it up and found
12" of sediment inside. How old is it it may be time to consider a new
one. You can try flushing it but it is probably so clogged if it is old
that you will never gat it clean. Unless flushed regularly tanks can
loose efficiency every year due to scale buildup