Need help for Ro/Di

[EGrfx]

What you are getting with your resin is about right with your RO. The truth is you are expecting more bang out of a 3 stage RO+DI. That RO system is primarily for drinking or fresh water tanks (less demanding). The main point of the stages prior to the membrane is to protect it. The primary job is to filter or breakdown as much as possible the impurities in the water before it gets to the membrane. It's pretty much standard now to at least have 3 stages before the membrane (sediment+carbon/gac+block carbon). With less stages the membrane will have to work harder and it will lessen the life. So what is happening your membrane is getting bombarded and it's letting the TDS slip through. The DI resin picks those up and that is why it is getting depleted quicker. For example those who have a water softener or has soft water to begin with in their homes will get more life out of their RO system and less frequent filter changes. By the time the water goes through all those stages it has been broken down of its chemicals and hardness that the membrane has less to flush out. Therefor the DI will last longer.

As far as RO goes, I consider the housing pretty much equal. What makes a good RO system is what's inside (i.e. quality membrane, sediment filter, carbon blocks and DI resin), those make the biggest difference and they're not created equal.

 

[AZDesertRat]

More prefilters is not better, there is absolutely no reason for two carbons. This goes back 25 years when filter technology was not what it is today.
Fewer, but better filters is the answer. A single low micron, absolute or near absolute rated sediment filter protecting a single 0.5, 0.6 or no larger than 1 micron extruded carbon block is by far the best choice. The 1 micron or smaller sediment filter is actually protecting the billions of tiny microscopic pores in the carbon when chlorine is adsorbed so it can do its work and last as it should. The reason some vendors still use two carbons is they use an inferior sediment filter so the first carbon is a sacrificial filter helping to trap what the sediment filter missed. Waste of your money and actually had higher headloss so the RO membrane is not as efficient.
No need for and GAC or so called chloramine carbons either if you follow the above, carbon does not remove chloramines anyway so another waste of your hard earned money. Spend your money on better replacement filters and a better DI cartridge which actually does help with chloramines if you have them. Carbon removes the chlorine portion of chloramines and breaks the bond with the ammonia portion which is mostly removed by a good high rejection rate RO membrane then polished off by the DI. Chloramine carbons are for industrial applications with extremely high chloramines like cooling towers, the EPA limits chloramines in drinking water to the same maximum level as chlorine at 4 mg/L which is a walk in the park for a single 0.5 micron carbon block and a full size vertical DI with fresh resin.