125mL of 10% phosphoric acid too much?

[ajdelange]

AJ, you seem to forget that RO operates on the basis of percentage removal. If the water supply has a lot of 'stuff' in it, the RO will also have a proportional amount of 'stuff' in it. Expecting zero for alkalinity is not feasible for many RO users.

The alkalinity of the RO water isn't going to be anything like 15 unless the membrane is old or damaged or the water is extremely alkaline. 0 is a better estimate.

For most people. If alkalinity is say 300 or more we might expect alkalinity of 15 at 95% rejection. Far, far more people have alkalinity below 100 than have it over 300. 0 is a better estimate. A cheap TDS meter is a good way to see if one is in the minority.

 

[day_trippr]

[...]A cheap TDS meter is a good way to see if one is in the minority.

And to that end I only have myself to blame for not seeing the obvious.
My TDS was showing 8.
Why I went with an RA of 15 anyway for two brews was stupidity in action...

Cheers!

 

[Silver_Is_Money]

Due to terrible well water with through the roof high everything, my homes RO has a measured TDS of 58 (116 uS/Cm). Based upon this I'm guestimating that my RO water has alkalinity of ~26 and bicarb of ~32. Do these values seem about right for RO water with a measured TDS of 58?

 

[JDL]

Looking forward to hearing reply on this as well. I am about to order my RO System and was wondering how to calculate the RA off the TDS.

Jeff

 

[ajdelange]

And to that end I only have myself to blame for not seeing the obvious.
My TDS was showing 8.
Why I went with an RA of 15 anyway for two brews was stupidity in action...

Wisdom is the state of understanding that comes from having experiences we wouldn't have if we were wise.

 

[ajdelange]

Due to terrible well water with through the roof high everything, my homes RO has a measured TDS of 58 (116 uS/Cm). Based upon this I'm guestimating that my RO water has alkalinity of ~26 and bicarb of ~32. Do these values seem about right for RO water with a measured TDS of 58?

For starters, 58 ppm as a TDS estimate does not seem very high. Were it all sodium chloride (and your meter calibrated for sodium chloride) you would have 1 mEq/L Na (23 mg/L) and 35 mg/L Cl-. Not RO water but not exactly 'terrible' either.

But, of course, your well water is probably a mix of sodium, chloride, sulfate, bicarbonate, calcium and magnesium ions with perhaps a little potassium. Conductivity measures the sum of conductivity contributions of all these ions and so it is impossible to tell what its composition is without other measurements. If the only thing in the water is temporary hardness then you could look up the conductivity of calcium bicarbonate solutions and determine how much is dissolved and then calculate hardness and alkalinity from that. Or assume that temporary hardness is the major contributor and bound alkalinity and hardness from that. But you well may have some permanent hardness, sodium, potassium, chloride...

Get hardness and alkakinity test kits. That's how to determine those two parameters.

 

[Silver_Is_Money]

For starters, 58 ppm as a TDS estimate does not seem very high. Were it all sodium chloride (and your meter calibrated for sodium chloride) you would have 1 mEq/L Na (23 mg/L) and 35 mg/L Cl-. Not RO water but not exactly 'terrible' either.
....

Get hardness and alkakinity test kits. That's how to determine those two parameters.

Per a GH/KH test kit, my wells alkalinity as CaCO3 is 436 ppm. And my wells total hardness (as calcium carbonate and/or magnesium carbonate) is 758 ppm.

GH = 42.5 drops into 5 ml (averaged over several quite consistent runs)
KH = 24.5 drops into 5 ml (averaged over several quite consistent runs)

The well water first goes through a softener, and then through an under the sink RO unit, and the RO comes out at 58 ppm TDS.

 

[ajdelange]

Check the drop in hardness going through your RO unit. Then apply the same rejection to you alkalinity. This will be rough as membranes reject different ions to a different extent. If you really want to know the alkalinity of your RO water, measure it.

The softener will bring the hardness of water run through it down to a couple of ppm. Thus the hardness of the RO system permeate should be near 0.

 

[Silver_Is_Money]

Check the drop in hardness going through your RO unit. Then apply the same rejection to you alkalinity. This will be rough as membranes reject different ions to a different extent. If you really want to know the alkalinity of your RO water, measure it.

The softener will bring the hardness of water run through it down to a couple of ppm. Thus the hardness of the RO system permeate should be near 0.

If the total hardness of my RO water is near zero, does that mean that the majority of my 58 TDS reading is alkalinity? I initially assumed that there must be a split between cations and anions, which totals to 58.

 

[ajdelange]

Whereas if previously you had mostly temporary hardness half would have been calcium, now it's sodium.