How bad is TDS 38 ?

[nystang]

I got an RO/DI unit and a TDS meter so I am measuring everything now. It shows that my tap water is 38ppm. How bad or good is it? The waste water from RO/DI unit shows 53ppm. I'm new to all TDS/RODI thing so I'm pretty excited. Until today I used distilled water for my tank but this is history. The RO/DI unit is not new but I got it for free and it is slightly used. The RODI water shows 0ppm.

[Tbone675]

38 is great. well water? my city water goes from 60-150ppm

[Old Gregg]

Pretty good. Mines around 45-55ish and I thought that was good

[nystang]

It is a city water. Bay Ridge, Brooklyn. I tested it a couple of times. It's always the same.

[Amphiprion1]

That's very good. Mine runs roughly 40 ppm and my filters last a good, long time. My membrane is going on 5 years and I still get 0 TDS out of it before it ever gets to the DI resin.

[Enigma]

I got an RO/DI unit and a TDS meter so I am measuring everything now. It shows that my tap water is 38ppm. How bad or good is it? The waste water from RO/DI unit shows 53ppm. I'm new to all TDS/RODI thing so I'm pretty excited. Until today I used distilled water for my tank but this is history. The RO/DI unit is not new but I got it for free and it is slightly used. The RODI water shows 0ppm.

 

The TDS reading in your tap water is excellent. The only problem is that you don't know what the dissolved solids are.

 

The TDS of my tap water here in Calgary is in the 280s. My ro/di gives me 0.

[iball1804]

I'm curious, what did your distilled water have TDS-wise?

[nystang]

The distilled water is 0 as well. I just returned from a friend of mine who lives in the same neighborhood and (of course) i measured his tap water. It was the same as mine. He also has a Brita filter on his faucet. The water after Brita read 17ppm, although it was used for some time. Interesting.

[iball1804]

Good, because I use distilled

[godfathernikki]

38 is awesome. Thats what my ro puts out, but my tap water is usually 500-700.

[AZDesertRat]

NY has low TDS but extremely high suspended solids (TSS), so much so the EPA is suing the water utilities and charging them daily fines until treatment plants are constructed and in operation to bring the levels within US EPA guidelines.

 

NY waters are a challenge for sediment filters as it plugs or fouls them quickly. Some vendors such as Spectrapure and Buckeye have developed pleated sediment filters in the 0.2-0.5 micron range which have 10x the surface area of normal spun ploy type filters so last much longer plus are washable a time or two if done properly to extend them even further.

[nystang]

The guy who gave me the RO/DI unit used to have a pico tank some time ago and he was aware of the high TSS in NY. That's why he bought this additional filter (the glass or rather acrylic/plexiglass) that he gave me as well. Unfortunately I forgot the name of it but you guys know it for sure. Here is a pic of my RO/DI plus this "mysterious" filter.

 

[AZDesertRat]

You will find my professional opinion on those little throw away RO/DI systems and their high costs and poor performance in ths thread.

http://www.nano-reef.com/forums/index.php?showtopic=306889

[nystang]

I'm not going to argue. I'm new to RO/DI business. This unit comes from Airwaterice. The guy who gave it to me, also upgraded one of the component so instead of 50 it is 150 if I remember correctly. As for the cost? I got it for free, so, so far I'm not loosing.

[AZDesertRat]

The 150 GPD membrane is one of the worst you can buy. It performed so poorly in testing many vendors discontinued it, I owned one myself personally and can speak from experience.

I also owned a Air Water Ice Typhoon III and was very disappointed in what was their top of the line system at that time. My DI lasted 150 gallons no matter what I tried, I even replaced the 75 GPD membrqane and had it factory tested. I sold that system and bought a MaxCap and my first DI lasted 830 measured gallons and its been over 1000 gallons per cartridge ever since. There really is a difference. You will pay close to the cost of a new system when you replace those filters and will continue to do so much more often than with a good system. Check your tap TDS, RO only TDS before DI and the final RO/DI TDS to see how yours is performing then compare those readings to a real RO/DI to get an idea what I am saying.

[nystang]

Tap water - 38

RO only before DI - 2

RODi - 0

 

What does it tell me?

[AZDesertRat]

It tells you your RO membrane is borderline shot at 94.7% efficiency. A good membrane will be 97-98% efficient and msot Spectrapure membranes will be 99+% efficient.

The reason this is important is for every 2% decrease in removal efficiency or rejection rate, you cut the life of your DI resin in half.

For a comparsion my tap water TDS is around 580 to 630 right now and my RO TDS is between 2 and 3, same as yours but my rejection rate is more like 99.43% last I calculated it. If my membrane were at 94.7% like yours my RO only TDS would more like 30 to 32. Thank your stars you have low tap water TDS.

 

Your DI is good at this point but watch your final TDS closely and change the DI cartridge as soon as you start seeing anything other than 0 TDS.

[nystang]

WOW. Thanks for the info. Now I understand. I think I'm very lucky that the tap water is pretty good AND the RO/DI system so far didn't cost me a dime. So what you are saying, if my RO/DI water will go up, let's say 1 or 2, I should exchange only DI cartridge?

[AZDesertRat]

At a minimum it is recommended you repleace the sediment and carbon filters every 6 months, this is with full size 10" filters and normal water quality. In your case with the extra sediment filter you would want to run no larger than a 1 micron replacement inside it and you could actually toss the small throw away sediment filter as everything you place inline in front of the RO membrane causes a head loss and lowers both the GPD and the rejection rate or efficiency.

Your carbon is more than likely GAC which is the absolute worst thing you can place in front of a RO membrane as carbon crumbles and turns to dust with usage as it abrades itself, it is very soft. This is probably one reason the membrane efficiency is down, it is plugging with carbon dust. 20 oz of GAC lasts approximately 300 gallons before it is exhausted in testing so you will get approximately 60 gallons of treated water per new GAC cartridge, very expensive water. If you can find thro away carbon blocks instead of the granular you would be money ahaead as it will probably last 1000 to 1500 total gallons or 200 to 300 treated gallons at the normal 4:1 waste ratio so less replacing and lower cost of operation. By comparison, if you were to buy an additional 10' clear cannister and a full size 0.5 or 0.6 micron carbon block you would get 20,000 total gallons per replacement or 4,000 treated gallons if you can keep the sediment and colloidal materials out of the billions of tiny microscopic pores that trap the chlorine, this is where a good sediment filter comes into play. As you can see, there are multiple levels of quality available and while the better quality costs more up front, the lifespan is many times longer so the cost goes down with time.

If you replace the GAC every 60 gallons at say $15 a pop versus spending $20 on a canister and $13 on a 0.5 micron carbon block which lasts 4,000 trated gallons the cost is much much less with the better components even though you spent more initially. On average, across the country, a quality RO/DI system produces treated water for about a nickel a gallon which includes the cost of replacement filters every 6 months, replacement DI resins and the water and sewer rates for both the treated ad the waste water flows. If you have to replace the carbon every 60 gallons at $15 the cost is already at 25 cents a gallon and you have not paid for the water or sewer bills or replaced the sediment filter and DI resins yet so its probaly 10x the cost. you really have to look at it from all angles, what seems like a good deal often isn't.

[nystang]

Thanks. It really gives me a different perspective.