RO Question

[7thheaven]

Hi all~

I chagned all my filter sediment, Pre,post carbon and RO membrain

My tap water is 93ppm with TDS but RO water is 18ppm...

I expect the RO value is under 10 but 18ppm!!!

The membrane is 150GPD...

If I changed RO from 150 to 75GPD, My RO level can be under

18ppm?

Thanks in advance

[Buckeye Hydro]

What is the factory spec rejection rate on the 150 gpd membrane?

What is your pressure?

Are you reading the TDS after or before the post carbon?

Russ @ BFS

[kylehca]

Would the TDS reading be more post carbon?

[7thheaven]

Thanks...

I do not know the pressure and rejection rate (I also wanna know the rejection rate but I can not find it in RO label)

I will check after post carbon and let you know... Thanks..

:)

[Mako]

If you move down to 75gpd filmtec your rejection rate will be much better, about 98%. Past 75gpd they fall down to 90%

I would expect your TDS to be below 10 with your setup though. What are you measuring TDS with? Probe clean? Cal recently?

[Buckeye Hydro]

The 150 gpd membranes available from BFS have the same rejection rate as the 75 gpd filmtec.

What is the brand of membrane you are using?

[7thheaven]

<a href=showthread.php?s=&postid=12419689#post12419689 target=_blank>Originally posted</a> by Mako
If you move down to 75gpd filmtec your rejection rate will be much better, about 98%. Past 75gpd they fall down to 90%

I would expect your TDS to be below 10 with your setup though. What are you measuring TDS with? Probe clean? Cal recently?


Thanks

I use this TDS

http://www.buckeyefieldsupply.com/ProductPhotos/Product_75.jpg imaged from BFS..

I recently bought it and I did not calibrate..

[Buckeye Hydro]

That's a good meter - called a TDS3 from HM Digital. I doubt that is the problem.

With an 81% rejection rate either you've not been careful taking the readings (for example - did you read TDS creep water?, use a "dirty" sample container? did you take the RO TDS reading after a carbon stage?), have very low pressure - too low for the membrane to work properly, or your membrane may be bad.

If you'll address these questions I can help:
1. Assuming your meter is ok, are you sure your TDS readings are accurate?
2. Did you take the RO reading immediately after the permeate port or did you let the permeate go through another filter stage or tank before you measured it?
3. Pressure is critical, especially with a 150 gpd membrane. You might want to think about a pressure gauge add on kit. We need to know how much pressure you have.

Russ

[7thheaven]

Hi~

I checked after post carbon value with TDS...

143.. WOW :(

(tap water is 93)

I flushed filters (sediment, pre, post carbon) several liters but

I think flushing need more...

How about your opinion?

[7thheaven]

Flushing more 1 hour. the AFTER post carbon TDS value is 94

(similar tap water....)

Until when I should flushing? Which value is proper after post carbon? (before RO mombrane)

[Buckeye Hydro]

I'm sorry seems like we are having trouble communicating.

[7thheaven]

<a href=showthread.php?s=&postid=12420010#post12420010 target=_blank>Originally posted</a> by BuckeyeFS
That's a good meter - called a TDS3 from HM Digital. I doubt that is the problem.

With an 81% rejection rate either you've not been careful taking the readings (for example - did you read TDS creep water?, use a "dirty" sample container? did you take the RO TDS reading after a carbon stage?), have very low pressure - too low for the membrane to work properly, or your membrane may be bad.

If you'll address these questions I can help:
1. Assuming your meter is ok, are you sure your TDS readings are accurate?
2. Did you take the RO reading immediately after the permeate port or did you let the permeate go through another filter stage or tank before you measured it?
3. Pressure is critical, especially with a 150 gpd membrane. You might want to think about a pressure gauge add on kit. We need to know how much pressure you have.

Russ

Hi Russ~
I am not good at english than Korean :)

1. I think TDS is OK.
2. I took the RO reading after go through another filter stage
(sediment, precarbon,post carbon)
3. I do not have pressure gauge so I do not know how much pressure I have

I am not sure my answer is enough.

I want to know which TDS value is OK before RO membrane in case tap water value is 93. Under 93?

[Buckeye Hydro]

Regarding your RO membrane and DI resin, use your TDS meter to measure, record, and track the TDS (expressed in parts per million) in three places:
1. Tap water
2. After the RO but before the DI
3. After the DI.

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 parts per million (ppm). Common readings are 100 to 400 ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block filter (collectively called prefilters) do very little to remove dissolved solids. So with your tap water at 400 ppm, you can measure the water at the “in” port on your RO housing and you'll see its still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 90% (i.e., they reject 90% of the dissolved solids in feed water). So the purified water coming from your 100 gpd membrane would be about 40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce less purified water (aka “permeate”), but have a higher rejection rate (96 to 98%). The life span of a RO membrane is dependant upon how much water you run through it, and how dirty the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the total dissolved solids (TDS) in the water coming in to the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce less water as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the 40 ppm water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1 ppm to 3 ppm, 5 ppm, and higher, you know that your resin needs to be replaced. Sometimes people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin “dirty” water. This will exhaust the resin quicker then would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal!

[7thheaven]

Thanks BFS~

I understand this very clear~!!

I will call at filter company and check the my 100GPD RO rejection rate...

Thanks again~!

[7thheaven]

Hi all~

I changed 75GPD filmtech filter and after RO value is 4!!!

WOW..I think my 150GPD filter is bad...

If Before RO value is 100PPM, Using 98% rejection rate filter makes 2PPM after RO?

[Buckeye Hydro]

correct