When I used mono, I replaced every 3 months regardless of use to prevent too much memory development. I no longer use mono, I use PowerPro braid on everything, except the downrigger rods are the strike causes a horrific amount of tension and I use Big game on that line only.
Capt. Craig Copeland
2013 Nautic Star 2110 Shallow Bay Boat
Nautic Star Boats Pro Staff (nauticstarboats.com)
Redneck Fish'n Jigs Pro Staff (redneckfishn.com)