RODI micron filter after 100 gallons?

I would check to see if the line outside is sucking mud in or what. I would be more worried that you are drink that stuff. Assuming you drink 8 glasses a day in roughly 200 days you have ingested that much dirt.

 

Looks like the water in your area contains a lot of iron. You might check with your water utility to confirm the hardness and iron content, you may be a good canidate for a water softener to reduce both.

Prefilters should easily last 6 months with good water conditions.
Make sure you are using a low micron filter otherwise the junk you are seeing will end up foulding the pores in the carbon block rendering it useless for chlorine removal and ruining the RO membrane. Thye make pleated low micron prefilters which have 10x the surface area and can be rinsed out a few times before needing replacing. Spectrapure and Buckeye Field Supply both sell them and they will last much longer and filter better with lower pressure drop so the membrane works better too.