I hand clean mine in hot water. I swish them around in a 5 gallon bucket as hard as i can, rinsing them over and over. it might be time consuming but i have been using the same three socks for like a year and a half now.
can it be your sand bed that is building up nirates to that level? I dont think u can take out all ur sand at once cause this will totally mess up ur system. maybe try siphoning out a little section at a time when u do your water changes..