Looks like your in Tucson, lived there for almost 20 years before moving to FL. Tucson water is known for being quite hard. Hard water contains high levels of calcium and magnesium, which can lead to mineral buildup on fixtures, appliances, and in pipes, which in turns leads to corrosion amongst other things. This is harder on the RODI unit so you may just expect to have some more replacements a little more frequently then what the manufacturer may state since they are probably going off averages but it will be unknown until you test it for yourself. This is assuming you are on city water and not well water. On that note it may be wise to install pressure meters between your units to track there wear if it doesn't already have that.
Also another topic of interest you may want to look into is if the city is still using chlorine to remove water contaminates or if they have switched to chloramines (as a lot are). If they have switched to chloramine that is something you need to know to tailor your filter as chloramines are more challenging to remove than chlorine. Carbon filters are less effective at removing chloramines because they require a longer contact time and a special type of carbon called catalytic carbon to break down the chloramines effectively. RO/DI systems that use standard carbon filters may not fully remove chloramines and Chloramines are toxic to fish and can cause stress, illness, or even death if they are present in high concentrations. They can damage the gills, disrupt the fish’s respiratory system, and interfere with the fish's ability to absorb oxygen.
