Acceptable TDS

[Frogfish]

Its my understanding that the 75 gpd membranes have a 96-98 % rejection rate. But that the 100 gpd ones are typically at 90%. I am seeing 90% in my 100 gpd unit but will switch it to a 75 the next time I need to replace it.

 

[AZDesertRat]

That is only true with Dow Filmtec membranes. The 75 Dow is rated at 75 GPD at 77 degrees and 50 psi. The 100 Dow is rated at 100 GPD at 77 degrees and 50 psi. The 100 is not intended fordrinking water in the USA and is in fact not a reverse osmosis (RO) membrane at all but is considered a nano filter which is one level of filtration below RO and may not remove all viruses and bacteria, things like cryptosporidium and giardia. The ANSI/NSF gives it a rating termed "For Pool and Spa Use" right from the manufacturer.
On the other hand the 75 GPD Dow is rated for drinking water.

Where things get confusing are with GE Water (Osmonics) and Applied Membranes RO membranes. Both sell what they call a 100 GPD membrane but in actual fact they are comparable to Dows in every way. The difference is GE and Applied say their membranes produce 100 GPD, BUT at 65 psi and 77 degrees F water, not 50 psi like Dow states. What this means is you lay the graphs over each other, a Dow 75, GE 100 and Applied 100 and you find they ALL produce 75 GPD at 50 psi, 90 GPD at 60 psi and 100 GPD at 65 psi and all at 96-98% rejection. Same thing just a different way of advertising is all.

The moral is stay away from the Dow Filmtec 100 GPD at all costs.
While we are on the subject there are noe some membranes on the market advertised at 150 GPD. Thye do work and they will produce 150 GPD but again thats at 65 psi which most of us do not have at the tap.I did own one of the 150 membranes and it worked well but the vendor I bought mine from quit carrying them because thye had too many quality control problems and could not get enough of them to pass their testing procedures.

 

[revhtree]

Hey gang concern here. My TDS out I my RO unit is 0 but my topoff water is showing 366! I keep my RO water in food grade containers. Any ideas?

 

[Trex]

Do you keep a lid on the top off container?

Do you ever clean it? If so, when is the last time?

Do you ever completely empty it, or is there always a bit of water in it?

 

[NC2WA]

Rev,

I assume this is a new thing? do we have a baseline number to go on?

 

[revhtree]

Never completely empty it. I tested water from my RO unit via a inline TDS meter and got a 0 reading. I used the hand held and filled a cup of straight water and got 1 reading. Filled up a new plastic jug straight from the ro unit and got a 15.

Crap how clean do you have to keep these containers?

 

[Eienna]

I'd empty and bleach the snot out of it, I were you.

 

[revhtree]

Well I tested reserve water from my food grade 160g container and from my 20g glass top off tank and they both were pushing 400 tds. Checked a bottle of water ang got 7! Lol.

 

[NC2WA]

hmmm....and if you collect RO water made directly from the RO unit into a cup and check TDS it is 0?

<I'm trying to isolate the problem> but it is sounding like something in the containers is leaching out something.

 

[revhtree]

It is 1 collected directly.

 

[rock_lobster]

thats crazy rev I would scrap that tank immediately and get a new one that is sealed. something could be leaching from the container or else there is an aerosol contaminant if not sealed.

 

[revhtree]

Well it's a total of 4 different containers and all different types of material. The only thing I can think of is that they are dirty. They look pretty clean. The small 5g jug was a jug that came from a company that sold saltwater. So after that was used it's been used just for water.

Will bleaching them kill everything?

 

[Eienna]

I'm gonna say it _should_ kill everything in the barrel. Let it sit for about 20 minutes with bleach all over it. Scrub and rinse well (but you already knew that!)

 

[revhtree]

Anymore input?

 

[Trex]

Personally, I would try some vinegar -- if there was any build up in that one container that used to have salt in it, should take care of it.


But, if you clean up the containers, and the TDS post DI (( before the containers )) reads zero I wouldn't be too concerned. Myself, I just test the post DI water in a glass that I know is clean (( and only use for this )) and use that TDS to judge if my water is pure. However, I just might test my container water tonight.

 

[DeadheadSC]

2 going in and 0 coming out

 

[powers2001]

You cannot test saltwater with a TDS meter. The range of most hobbyist grade TDS meters is 999 TDS and some may have a high range which can measure up to 10,000 by tens so are not as accurate in the high range. Saltwater in your tank is easily going to exceed 30,000-35,000 which is way out of range and can contaminate the probe on a TDS meter if it is not cleaned with DI right away.

You say this can contaminate the probe if not cleaned right away. Will this ruin the probe?

 

[AZDesertRat]

Not as long as you clean it right away with distilled or RO/DI water. You always want to triple rinse the meter with either one before capping it and putting it away clean for next use. Once you start getting a build up of solids on the probe it is hard to calibrate and will not be accurate.

 

[Koaboy]

Revhtree, even though your picking up a reading, I'm wondering if there is a way to test what it is in your water. Might be safer than what the city puts in it, lol. The risk involved in using agents to clean the container may outweigh the benefits.

 

[Marc West]

Yes up in Suwanee near Lake Lanier our Tap TDS is 38, pre DI is 2 and post is 0. by the time it passes through 5 people down in Atlanta city its higher.