The proper means to establish when a disposable cartridge needs to be replaced is by pressure loss across the filter. That is when it reaches 15 psi. All other means are wasting your money, especially using how it looks. And... in the vast majority of cases, disposable cartridge "whole house" filters are a waste of money. What you're trapping in that cartridge is ferric iron (household rust) which is due to oxidizing ferrous iron in the cartridge due to the DO (dissolved oxygen) in the water. And it's not a problem except in the toilet tanks when you look in them, and most folks usually don't for months at a time because there is not reason to as long as the toilet flushes and the water is clear. That includes ahead of a softener, unless it is a Kinetico non-electric centuries old water powered softener.
From the looks of the cartridge, I say you have a ferrous iron problem with the water and you should have a water analysis done. And based on the data, you probably need a softener or iron filter.
Quality Water Associates