Advice is to backwash before pressure up 25%. For this old filter / glass that would be 1.25 * 17 or 21.
So have been watching the pressure and it never goes up. Finally yesterday after 3 months I saw 19 so backwashed.
The water was really brown. See pic below.
Pool water is clear.
1) I suppose should just bwash q month regardless of pressure. True?
2) Why does pressure not rise in this old device?
3) Since the water was so dirty, was I actually filtering anything? Or just putting debris back into the water and wasting pump electricity $$?