Stan,
I keep using it without filtering until the solution is just ugly as can be, think brown pond water. The dirt and grime settle to the bottom of the tank so I do not think they act as an abrasive. I have never noticed any harm from the dirty water. I only put just a couple of table spoons of chemcrest 235 in tank. The gallon of concentrate I have now is still about 1/4 full and I bought it 4 years ago. Pretty reasonable over time.
Steve

http://www.bertramandco.com/
Booking African hunts, firearms import services

Here for the meltdowns