Just trying to explain. The key word there is trying. Pretty confusing when some ppl recommend changing membrane every four months, and others say they haven’t changed in nearly a decade without issue. It takes no time for chlorine to burn your membrane through chemical attack. If your water source has little chlorine changing your carbon block is not that important in terms of protecting the membrane. If you have lots of chlorine changing once a year or even every six months may not be enough.
And yes I understand chlorine isn’t the only thing carbon removes. The membrane will remove chlorine too. Although it will be damaged in the process.
And it is pretty easy to test for chlorine with a test strip. Would recommend first testing your water source so you know what you’re up against.
As an example, in my home the 1 micron sediment filter is still clean, while my carbon block is exhausted. So changing the carbon when sediment filter is visibly dirty is not a good practice for me.