when to change RO membrane

[Buckeye Field Supply]

Thanks Reefin101!

 

[reefin101]

See how long your DI resin lasts with the current membrane. Price out a new membrane.
Figure out which is more cost effective for you.

This question has been asked and answered many times on the reef forums.
Dow Filmtec membranes may or may not be 98% rejection rate although this is what they strive for. years of lab testing finds most out of the box, brand new are closer to 96-97%. You need to remember, every 2% you lose, you cut the life of your DI resin in half so a 4-6% decrease can add up quickly f you make much water. My off the shelf 75 GPD Dow Filmtec gave me a RO only TDS between 13 and 15, I switched to a hand tested Spectrapure Select series and that 13-15 TDS is now between 2 and 3 using a calibrated COM-100 handheld TDS meter. I have two dual inlines but rarely even tunr them on as the yare in no way as accurate or reliable as a handheld for the same $25. Don't waste money on inlines.

The time to change a RO membrane is when the cost of DI resin starts going up at which time you would be better off with a new high rejection rate RO membrane which could extend the DI resin life by several times for a cost savings and better water quality. For me personally, I use 96% rejection as my change out point as resin starts costing more tyhan the replacement membrane. My current membrane is 4.5 years old and my rejection rate is around 99.4% still to this day.

I will look into a nice hand held..Thanks.......

Well i looked back and I was typically changing out one of my dual DI's every 9 mos.....
I just changed my DI and 3 prefilter on 7-1-12 and that was 2200gal ago. I have only used about 1/3 of my first DI canister. So really about the same as before. As it will be about 7-8mos and I will have to refill a DI cartride.

oh and when #1 DI is done, I swap # 2 DI to # 1's spot and put all new fresh in #2 spot....

So I guess no need to change the membrane

 

[AZDesertRat]

Thats great!

 

[Gato 1]

If you want to check membrane performance:​

Use this formula:

Rejection Rate (%)=(Feed Water TDS−RO Water TDSFeed Water TDS)×100\text{Rejection Rate (\%)} = \left( \frac{\text{Feed Water TDS} - \text{RO Water TDS}}{\text{Feed Water TDS}} \right) \times 100Rejection Rate (%)=(Feed Water TDSFeed Water TDS−RO Water TDS)×100
Example:

• Feed water TDS = 300 ppm
• RO water TDS = 15 ppm

(300−15300)×100=95%\left( \frac{300-15}{300} \right) \times 100 = 95\%(300300−15)×100=95%
Typical guidelines:

• 96-99% = Excellent
• 90-95% = Aging membrane
• Below 90% = Usually time to replace
• se this formula: