RO/DI replacements

I have the typhoon III from air water ice, and it's time to replace the filters. I am ordering the replacement pack from them, but my question is if I have to replace the membrane on a yearly basis, or just the filter pack?

 

Probably just the prefiler and carbon.
A TDS meter will tell you if the membrane is in ned of replacement. You need three TDS readings to troubleshoot a system, tap water TDS, RO only TDS and final RO/DI TDS.
The RO TDS should be 95-98% less than the tap water TDS, if not it may be time for a membrane. Usually a membrane will last 18 months to 3 years or more if you keep up with the other filter replacements on a 6 month shcedule and disinfect the system at that time or at least annually. The TDS meter does not help you here so stick with 6 month intervals.

The RO/DI TDS should be 0. If not you need a DI replacement too.

 

I have the same one...I only replace the filter cartriges....my TDS is 0 so the membrane is good. I think the membrane will last 3-5 years depending on your use.

 

Just because your TDS is 0 does not mean the membrane is good, it means the DI is good. Many people often overlook the RO membrane performance which is a critical piece, actually the most critical piece. It can be bad or performing poorly and the DI then acts like a crutch to prop it up. DI gets expensive like this since it needs replacing much more frequently. A little known rule of thumb says "For every 2% you increase the membranes efficiency, you DOUBLE the life of your DI resin."

This can be a significant savings just by replacing a poorly performing membrane with a new better perfroming one for $30 or $40. It does not take many DI replacements to pay for a new membrane. Always test all three point, tap water, RO only and RO/DI often.

 

On the website, the filter replacement pack is the same price as the membrane alone. Could I just replace everything once a year? That would run me about 80 dollars a year, so it would not be killer financially, the concern is whether or not it will give me clean water.

 

No need.
The prefilter and carbon have absolutely noting to do with final water quality, they are there to protect the RO membrane which is the workhorse of the system and can last for years it takne care of with quality, timely filter replacements.
One suggestion I would make is go with their optional low micron replacements, they do a much better job of protecting the membrane.