RO membrane

How do you know when its time to change your RO membrane? Are they good for a certain amount of time or is it dependent on how many gallons of water they have filtered? I change my 3 pre-filter cartridges about once per year. Is this sufficient?

 

generally I change my carbon and sediment every 4 to 6 months..and the membrane is good for a couple years ..that's all variable though..whats your TDS...
bump..

 

You change the membrane either when the rejection rate or removal efficiency is no longer in the 95-98% range and DI resin replacements start exceeding the cost of a new membrane or when the GPD starts dropping off due to plugging or fouling or both.
Often a membrane will start producing less due to insufficient waste ratio which is the only way a membrane gets flushed properly and eventually the membrane fabric can burst or be compromised such that the TDS goes up dramatically.

Changing the sediment and , ensuring th ewaste ratio is close to 4:1 waste to treated and disinfecting the system at least annually go a long way for membrane life. With a good system using high quality replacements it is not unheard of to get 10 years or very heavy usage out of a membrane. I am over 4 years on my Spectrapure membrane and am still getting over 90 GPD at 99.43% rejection rate or removal efficiency and all I do is make sure the waste ratio is correct, disinfect the system as directed and make sure the filters are in good condition. Like a fine tool, take care of it and it will last many many years.

 

You both mentioned TDS. how do I measure this?

 

Total Dissolved Solids, basically all minerals or solutes dissolved in the pure water. This is why you buy a RO or RO/DI system, to remove those contaminants from the water leaving only pure H2o.

You measure TDS with a TDS meter, preferrably a handheld meter such as the HM Digital TDS-3, TDS-4TM or COM-100 or equal costing between $20 and $60. A TDS meter works by measuring the conductivity of the water. Since pure water is not electrically conductive, the dirtier the water the more conductive it will be, the more pure it is, meaning the better your RO membrane and DI resin are working, the lower the TDS or less conductive it is.

It is almost impossible to know how well a RO or RO/DI is performing without a TDS or conductivity meter.

 

Most useful. That is the information I was looking for. I will start shopping around for a TDS meter. Can you suggest a good quality brand for me?

 

He did!lol, i have the HM brand and its cheap and great! Measures the same as the local water manufacturers $1000 one does!

 

I suggested the best three you can buy above.
You can get them from places like ww.buckeyefieldsupply.com or SpectraPure Water Purification Products starting at about $20-$25.
Some will suggest inline type meters but they have serious limitations such as lower accuracy and limited uses since they are dedicated to two places and cannot be used portable like a handheld meter. To test or troubleshoot a RO/DI system you need three readings, not just two so you would need two dual inlines and they still would not be accurate since they are not temperature compensated and actually sense air temp and not water temp.

 

Would this suffice?

http://www.marinedepot.com/HM_Digit...iums-HM_Digital_Inc.-HB00045-FITEMOMI-vi.html

 

That is the TDS-4TM I suggested already. Good meter.