Poll: Do You Know Your TDS?

[XNavyDiver]

That is a great question, I was kind of wondering the same thing..Is there like a calibration fluid that has a known TDS that you can use like a refractometer has a 35ppm solution to calibrate?

Yeah, a known standard. I guess it's off to Google to find out...

 

[Crabs McJones]

Yes, there is TDS calibration fluid.

https://www.bulkreefsupply.com/tds-342-calibration-solution.html

Well look at that! Thank you

 

[XNavyDiver]

Ok, so is there a way to adjust our TDS meters to read a known TDS solution if ours are reading something different? Like a refractometer. Im not sure if mine has an "adjustment" feature to the meter.

 

[revhtree]

Bad business not to know your TDS! Or should I say it's algae business!

 

[XNavyDiver]

So I you tubed this and it's fairly straight forward process for those with the hand held pen type of meter. Mine is the mounted display type that is plumped into the lines. I'm guessing disassembly is the only way to do this. I'm going to have to take a closer look at my meter and see if it has a calibration set screw in the display body.

 

[Signalhead]

I live in Florida and use well water. My TDS directly from the well head is about 900, coming into the house after areator and softener is 700 to 750. That's going into my RODI, out is 0 anything higher than 10 I like to change the resing. Replace my filters twice a year. Use a meter in the in and out. Also us a hand held to verify.

 

[dbl]

Mine varies from 180-225 out of the tap but ends up at 0 after RO/DI process.

And yes, I highly recommend having a handheld TDS meter. Although I use the inline meters on my system, from everything I've read, the inline meters are not as accurate as the handheld versions. So I double check my output every once in a while (probably not enough) just to make sure all is working properly.

 

[flagg37]

I thought my tap tds was bad at around 400, some of you are way worse. I read somewhere that the legal limit was 500.

 

[Chuk]

I thought my tap tds was bad at around 400, some of you are way worse. I read somewhere that the legal limit was 500.

It’s a secondary standard aka recommendation not an actual legal requirement. Well waters also have different standards than surface waters

 

[NY_Caveman]

How would you determine if a TDS meter is giving a false reading?

For me, I usually test my meter before using on two known sources, distilled water and on my own tap water. It always reads store bought distilled water as 0 and my tap after running for a couple of minutes is usually 38. Not scientific probably, but fairly reliable.

 

[melev]

Very cool thread. Made me go check some of my own RO/DI storage reservoirs, something I've not done in a long time.

Tap water today: 122
TDS coming out of the membrane: 2
TDS coming out of the DI: 0

Then I scooped some water out of this ATO reservoir that I built in 2010 and installed under the 400g. I have absolutely no way to clean this container, but it stays sealed shut 99.8% of the time. I've opened the access door maybe 6 times in the past 7 years to install the top off pump, or adjust the float valve. My goal is to keep this vessel pristine, because the only way it comes out is if I remove the sump first (unlikely) or I cut it out with a sawsall in pieces because there's only 3/4" of space above it -- in other words it can't come out.

The TDS over that water measures 2, which I'm totally fine with. It is refilled once a week with 0 TDS water.

Then I checked the TDS of the ATO reservoir of my frag system as well, and it measures 1. This one I could remove for cleaning, but I don't see a reason to do so.

 

[lou dog420]

I'm on well water, and I have a RO/DI unit. I have never tested the TDS straight from the tap but I have a dual TDS meter that measures before and after the DI resin. Effluent from the RO measures 2 TDS, 0 after the DI. Always 0!!

 

[Chuk]

No point messing it with it if its only 1 or 2. If your turnover is high (<1 week) the TDS creep should be pretty low . This is really only be a concern if you have a large volume like a mixing station type thing as a reservoir and you are going 2+ weeks or so without refilling the reservoir.

 

[sghera64]

My incoming water is about 350-420 ppm (lower in spring higher in winter). I feed softened water to my RO membrane. Product water is generally 0-1 ppm TDS. I typically see 99.5+% rejection. I use a simple trick to keep my membranes producing this quality water. Current membrane is >2 yrs old.

I removed my DI canisters about 18 months ago. Upon testing the water that comes out of the RO membrane is maybe 0.009 - 0.020 ppm PO4. BUT! all my top-off water flows through a highly alkaline Neilson reactor (Kalkwasser). That kind of high pH knocks the PO4 way down. The 2-3 ppm TDS water that comes out of the holding tank (likely CO2--> HCO3+) does tend to make a bunch of insoluble carbonates that accumulate at the bottom of the Neilson reactor. I have to flow this out 1x / week. I struggle to keep any PO4 in my reef tank: either the kalkwasser removes it, the coral do, or the macro algae do). Additionally, there was an article written a number of years back (maybe by Randy H-F) showing how high pH water (kalkwasser) can reduce and remove some metals (iron, copper). That's why I no longer shoot for 0TDS-water and save time/money by simply using a high quality RO-only system.


RO membrain (pun) care: I have a Spectrapure 90-GPD system. I use a booster pump and supply 78psig to the membrane. I pretreat the incoming water to the RO membrane like this:

• Softened water is fed to the unit
• GE's ROSave.Z depth filter
• 3x BRS Universal 1-micron carbon blocks in series (I test for Total Chlorine and Free Chlorine breakthrough 2x / yr)
• SpectraPure Standard 90-GPD RO membrane (MEM-0090) touting 96-98% rejection.

Use and post-use routine:

• I run the unit about 1x/ week for 8-12 hours depending on need on Saturdays or Sunday's only.
• I run the product to waste for 10-20 minutes at the start: until TDS of product water is 1PPM-TDS or less (Using stock HM TDS meter to measure).
• I always flush across (by-pass open) and then through the membrane for 1-3 minutes after use with my product water from the water reservoir (typically 2-3PPM-TDS water)
  • I do this until the feed water reads 2-3PPM and the product water returns to 0PPM.
• Every Monday, Tuesday and Wednesday, the system automatically turns on for 1 minute and feeds 2-3PPM-TDS water across the membrane at 6AM and 4PM.
• Every Thursday-Sunday the system automatically turns on for 1 minute and feeds 2-3PPM-TDS water across the membrane at 6AM.
  • My theory is that any chlorine that might impregnate the polypropylene membrane will seek to diffuse back out into the less chlorinated product water surrounding the membrane from back-flushing. Repeating this drives the process continually. No chlorine means no holes in the membrane for it to start leaking through larger molecules.

Does anyone else have a special routine before, during and after water collection from their RO system?

 

[Daltrey]

Yes I know the tds coming into and the tds going out. You can pick up a simple $20 meter that takes 5 minutes to hook up to your rodi system.

Tds in

Tds out

And if your using holding tanks like I do don't forget to test them with a handheld meter also.

 

[melev]

My incoming water is about 350-420 ppm (lower in spring higher in winter). I feed softened water to my RO membrane. Product water is generally 0-1 ppm TDS. I typically see 99.5+% rejection. I use a simple trick to keep my membranes producing this quality water. Current membrane is >2 yrs old.

I removed my DI canisters about 18 months ago. Upon testing the water that comes out of the RO membrane is maybe 0.009 - 0.020 ppm PO4. BUT! all my top-off water flows through a highly alkaline Neilson reactor (Kalkwasser). That kind of high pH knocks the PO4 way down. The 2-3 ppm TDS water that comes out of the holding tank (likely CO2--> HCO3+) does tend to make a bunch of insoluble carbonates that accumulate at the bottom of the Neilson reactor. I have to flow this out 1x / week. I struggle to keep any PO4 in my reef tank: either the kalkwasser removes it, the coral do, or the macro algae do). Additionally, there was an article written a number of years back (maybe by Randy H-F) showing how high pH water (kalkwasser) can reduce and remove some metals (iron, copper). That's why I no longer shoot for 0TDS-water and save time/money by simply using a high quality RO-only system.


RO membrain (pun) care: I have a Spectrapure 90-GPD system. I use a booster pump and supply 78psig to the membrane. I pretreat the incoming water to the RO membrane like this:

• Softened water is fed to the unit
• GE's ROSave.Z depth filter
• 3x BRS Universal 1-micron carbon blocks in series (I test for Total Chlorine and Free Chlorine breakthrough 2x / yr)
• SpectraPure Standard 90-GPD RO membrane (MEM-0090) touting 96-98% rejection.

Use and post-use routine:

• I run the unit about 1x/ week for 8-12 hours depending on need on Saturdays or Sunday's only.
• I run the product to waste for 10-20 minutes at the start: until TDS of product water is 1PPM-TDS or less (Using stock HM TDS meter to measure).
• I always flush across (by-pass open) and then through the membrane for 1-3 minutes after use with my product water from the water reservoir (typically 2-3PPM-TDS water)
  • I do this until the feed water reads 2-3PPM and the product water returns to 0PPM.
• Every Monday, Tuesday and Wednesday, the system automatically turns on for 1 minute and feeds 2-3PPM-TDS water across the membrane at 6AM and 4PM.
• Every Thursday-Sunday the system automatically turns on for 1 minute and feeds 2-3PPM-TDS water across the membrane at 6AM.
  • My theory is that any chlorine that might impregnate the polypropylene membrane will seek to diffuse back out into the less chlorinated product water surrounding the membrane from back-flushing. Repeating this drives the process continually. No chlorine means no holes in the membrane for it to start leaking through larger molecules.

Does anyone else have a special routine before, during and after water collection from their RO system?

That's a heck of a routine.

A few years ago, I had a brief scare measuring PO4 in my DI water until I realized it was the tester I was using. I broke out a couple of Phosphate titration brands and both measured 0, and I realized I was mentally over-reacting -- that all was indeed still as it should be and I didn't have to fear my water.

I don't see why you'd need to run it for 10-20 minutes initially. Usually within 2 minutes you've flushed the water off the membrane within the first 90 seconds. And you mentioned you have a flush kit as well, which only needs to be open for 15 seconds rather than 1-3 minutes.

But if this works for you, don't change a thing.

 

[Jason mack]

My tap water is around 183 tds but it has been higher .. out my rodi it is 0 if it starts getting 1-2 then I change the resin .. I should also say I’m from Rotterdam / Holland

 

[Randy Holmes-Farley]

FWIW, I've never been a fan of worrying much about how well an inline TDS meter measures TDS accurately or not. I know some disagree, but I have never heard of a convincing reason to worry about it.

The reason is that, assuming the meter works at all, that the error is ALWAYS a slope error. Any TDS meter will read 0 ppm TDS in air, so it is only the slope that will be off.

So if it is reading 50 ppm when it is really 100 ppm TDS, is that an issue? That would mean that 2 ppm TDS reads as 1 ppm TDS. I'd contend that is not really a concern.

If you respond to a rise in TDS to replace the DI (as most recommend, including me), then as soon as you see 1 ppm TDS or more, it is time to replace the DI (or the last DI in the series if you have 2 or more), and it doesn't matter exactly what TDS level you really did that at.

 

[Potatohead]

This has to be the most lop-sided poll ever. lol

My tap water TDS is only 14. Resin lasts forever

 

[NY_Caveman]

Here are some stats so far. The first set shows what people use regardless of if they know their TDS. The second set shows who knows and who does not: