Next I will talk about pre-filters, both sediment and carbon blocks. Depending on the sediment content of your water, the minimum micron rating you want to run on sediment pre-filter is 1 micron with .5 micron being optimal. Most of what you see for sale as replacement cartridges are 5 micron which is not the greatest. When you use a 5 micron especially if you have a sediment problem, anything smaller than 5 micron passes through the sediment cartridge and ends up on the next stage which is the carbon block which ends up clogging the carbon block and effecting overall system performance. With a carbon the micron rating is even more important as this is the protector of your membrane. A .5 micron carbon block is a MUST HAVE for your system. Not only will it trap any leftover particulate matter that your sediment filter may have missed, if you are using larger than a .5 micron sediment filter that is which in return will extend the life of your membrane to over 5 years or more. A .5 micron carbon block is much more effective at chlorine removal that a 1 or 5 micron cartridge. Chlorine kills membranes…period. A .5 micron carbon block handles a staggering 20,000 gallons of chlorinated water, a 1 or 5 micron only treats 5-10,000 gallons. A .5 micron carbon block only cost at most $3-5 dollars more. I also see no benefit in systems that have dual carbon blocks as a quality single .5 micron cartridge will do you just fine in even the most heavily treated chlorine areas. If you have a system that runs dual carbon blocks, I suggest re-routing that canister so that you can use it for another DI chamber. With a combination of a .5 micron sediment and .5 micron carbon block you can and will get a much longer life out of your membrane. Well over 2x the life of using 5 micron cartridges.
DI Resin is something that needs to be talked about as all resin is not created equal. If you are purchasing a RODI system I strongly recommend a unit that has 2 DI canisters. The first unit should be a standard resin on the cheaper side or even a refining resin that handles a ton of volume. And the final resin should be a quality High Silicate removal resin. The Idea of two resins is that the first chamber of resin will take a brunt of the silicate removal; this resin can be cheaper bulk or refillable resin. The second chamber will be a for removing the slight traces of silicates that may be left. With this method, you will only be spending a little bit extra on resin replacement as the second canister will last you a very long time as it is only removing trace silicates and can probably pass close to 3-5000 gallons of water before it needs to be replaced. There are companies out there that make high capacity resins that would be great for the first DI stage. Spectrapure makes a MaxCap resin that is super high capacity. I personally run about 2500 gallons of water through it before it needs to be replaced. With using the high volume resin I get 3x the capacity on my downstream resin. Avoid systems that do not have full size DI canisters. The small piggy back type canisters are a joke, expensive to replace and there are no real good options for resin for them.