Life expectancy of RO filter

[tom39]

I started in the hobby about May of 2013 and that is when I put my current RODI into service. My first tank was a Marineland 50g corner and the evaporation rate was about 1.25g/day. I did regular water changes that were 10g every 2 weeks and I kept that tank for about 4 years before I shut it down and set up my current 150g cube. For that tank I keep roughly the same schedule of water changes but due to its size I have an increase in evaporation of about 1.5 to 2 gal/day. In addition to those 2 tanks, over the years I have had a number of additional tanks and setups, all of which increased my water usage. By my calculations (very rough estimate) I have made about 6,500 gallons of RODI in the past 6.5yrs and I never make less than 50g at a time. Additionally, I always flush my RO filters for about 5-7min at the start of processing a batch of water. 

 

Anyway, the point of all of this is that I was wondering how long a RO filter typically lasts. My RODI is a 200g/day setup with a single 5 micron sediment filter, dual 5 micron carbon stages, dual 100gal/day RO filters (piggybacked) and lastly a dual DI stage. My current TDS numbers at the output of the RO's are 1 TDS for the first RO and 2 TDS coming out the second RO, this is with a source input water at about 100-110 TDS average. I believe that the second RO is only this high because this filter is reprocessing the waste water from the first RO filter. With the filters currently making a max of only 2 TDS, at this rate I cannot foresee the replacement of these filters for many years to come. 

 

My questions are:

What TDS numbers are others getting out of their RO filters?

How long has their current RO filter been in service?

How often are you replacing your RO filter?

What brand of RO filter are you using?

How much water do you make at a time?

Do you use a flush kit?

 

Thanks in advance

Tom

 

 

 

 

 

[treesprite]

Air,Water, Ice website says 3 to 5 years. 

[ReefdUp]

I'm much more simplistic - it's all measured and done by math. I have pressure gauges and TDS meters to identify pressure drops across stages and decreased performance. TDS measured before and after the membranes is compared against the proper rejection rate for the membrane (I forget the number off the top of my head for a 100gpd, but you can Google it if you don't know.) 

[tom39]

34 minutes ago, ReefdUp said:

I'm much more simplistic - it's all measured and done by math. I have pressure gauges and TDS meters to identify pressure drops across stages and decreased performance. TDS measured before and after the membranes is compared against the proper rejection rate for the membrane (I forget the number off the top of my head for a 100gpd, but you can Google it if you don't know.) 

I love your method and your thought process.

 

OK, so I am currently processing water and this is what I am able to achieve with my system at this moment. If you would not mind, please let me know if my thought process is off.

 

TDS coming in from city water supply is 77 TDS

Pressure coming in from the city water supply and feeding the 1st RO filter is 66psi

Pressure coming out of the 1st RO and entering the 2nd RO filter is 60psi 

Product water TDS coming out of the 1st RO filter - 1 TDS **

Product water TDS coming out of the 2nd RO filter - 1 TDS * / ** / ***

* Unfortunately I do not have a TDS reading of the water coming from the waste line that is feeding the 2nd RO filter.

** The numbers coming out of the RO this morning I am attributing to the low TDS from the city water source and the fact that my RODI has been making water since 5 pm yesterday and I have flushed the RO membranes 2x since starting the process. Normally the source water is 100-110 tds and I usually get a product water from the RO's of about 2 tds.

*** Note that is RO filter is the newest of the 2 and has processed about 1000g less water than the 1st RO filter  

 

So with the RO's reducing the TDS from 77tds to 1tds the rejection rate is 98.7%. Both of my filters are DOW filmtec 100gpd RO filters (not sure if they are the high rejection filters), so  using the acceptable rejection rate in the spec, technically I would be good to continue to use the filters until I reach a TDS reading at the output of 7.7tds. That is if the input water source remained at the current value 77tds.

 

The spec says that:

Filter model: DOW Filmtec TW30-1812-100 TFM100 membrane, TW-30-1812-100HR for High Rejection.

Size: 11.75" x 1.8"

Flow Rate: 100 gallons per day @ 60 psi water pressure

Average NaCl Rejection rate: 90% rejection rate for regular, and 98% for High Rejection.

 

Thank you,

Tom

 

[ReefdUp]

First, I'd looove city water with that low of TDS. Just that alone will extend the life of your filters. That's why I love pressure and TDS measurements versus time or volume measurements. My water is not as great.

 

Second, getting to 1 TDS post first and second RO is pretty much within the noise (and that's before DI!) I would guess you've got plenty of life on them. The DI will handle the rest. 

 

Fwiw, I usually end up changing my membrane every 3 years. That's not usually because I need it, but because we move, so the filters would go bad during storage. I have had 300-1000g of tanks, both in humid and desert climates. I think the city water in Las Vegas was 400+ when we were there... ewwwww.

[Origami]

Tom, the rejection ratio on your membranes indicates that they're still functioning very well. And, yes, the reason that you have higher TDS coming out of the second membrane is because it's processing the waste water from the first.

 

Your overall TDS is also low enough that you'll probably exhaust your DI resin pretty slowly, too. This is the same experience that I had while on city water in Ashburn.