RODI filter changes

[new2u]

I'm looking at buying a used RODI unit from a guy that says hes run around 500 gallons on it, should i change any of the filteres or the DI cartradges? I dont want to buy something that i have to mess around with i can get new for cheaper

 

[bigarn]

Ask when he last changed them out. I think rule of thumb is about every 6 months, same as for lights.