Funny these filters threads are popping up. I changed mine this morning as was going to put a thread on about not leaving them too long.
I usually change mine every 3 months, this time I left these in for about 6 months. Look at the inside of the pre filter, all that crap is now heading for the membranes, making their life a lot shorter. Makes sense to me to get back to changing every 3 months, maybe even sooner.
Also photos are under kitchen light, they look even worse under natural light.

