While I'm somewhat patiently (OK, not so patiently) waiting for my Linea Micra to arrive, I've been getting a few details sorted out. One detail is getting an easy process for making rpavlis water figured out. We have a whole-house water softener, and a Rayne Eradicator undersink RO system in the kitchen (which I believe is a Pentair GRO-2550). I'm using RO water as the base for the rpavlis water.

I purchased a 1000ml glass bottle for making concentrate and two 2000ml bottles for making water. I weighed out 1000ml of water in the small bottle and added to that 10g of potassium bicarbonate. In each of the large bottles I weighed out 2000ml water and added to that 20ml of the potassium bicarbonate concentrate from the small bottle. Sound OK?

For reference, here's what my TDS meter is reporting:

- Kitchen tap water (softened but not filtered): 169ppm
- RO water from the filter tap: 9ppm
- RPavlis water: 14ppm
- for fun, the concentrate: 3,260ppm

Do these numbers and this process sound OK?

Thanks,
John

The recipe math looks fine - - it's simple recipe algebra ...

Given: Full strength rpavlis is 100 mg/liter potassium bicarbonate
Your concentrate, 10 gram (10,000 mg) in the 1000 ml bottle contains 10 mg/ml
Diluting 20 ml of that concentrate to 2 liters gives you 10 mg/ml * 20 ml = 200 mg in a 2 liter bottle, which is 100 mg/liter

If got your mineral additions right, you added 100 mg/l of potassum bicarbonate to your 9 mg/l RO water to have an actual TDS of 109 ppm. But TDS meters measure conductivity rather than actual TDS. The reading they give you can be far off from actual TDS depending on the conductivity of the particular minerals in the water, the temperature of the water, and how the TDS meter is calibrated. Potassium bicarbonate is known to be less conductive than NaCl, and for an inexpensive NaCl calibrated TDS meter, measuring your RO water with 100 mg/L potassium bicarbonate added, measured at 25 ℃, you expect a reading in the 70 ppm ballpark. If you only measure 14 ppm that seems way low. Try again, and at or near the proper temperature. If you don't get in the ballpark of 70 ppm then the meter may be faulty or you may have gotten something wrong in making your mix.

Make sure you are using pure potassium bicarbonate (KHCO3)*
Make sure to shake the concentrate bottles well and give the salts a while to dissolve before adding to final mix
Before measuring the final mix TDS, give it a shake, use that to rinse the measuring container then pour a sample into the container for measuring. Let it warm up to 25 ℃ ( 77 ℉) before taking a measurement

*[edit addition] I see from the picture that you are using "Pure" brand potassium bicarbonate which appears to actually be pure. Their dosage statement: "Potassium Bicarbonate Dosage: 1/4 level teaspoon (1 g or 1,000 mg) contains 390 mg of potassium RDI" is consistent with pure 100% KHCO3 (1000 mg KHCO3 contains 390 mg of elemental potassium.)

My Linea Micra arrives tomorrow, so I wanted to revisit this to make sure I'm comfortable with what I'm about to put in it. I wasn't 100% confident in the results I was getting from just the "el cheapo" TDS meter I purchased on Amazon, so I bought an API GH & KH test kit, and ran some additional tests. I tested (1) tap water from the kitchen tap (treated with whole-house water softener), (2) RO water from filter faucet, (3) RPavlis water made per recipe in post 1 above, and (4) a bottle of "Perfect Coffee Water" I made using one of their packets mixed into a gallon of RO water. I tested GH and KH with the API test kit, and also tested TDS using the Amazon TDS meter. Here are the results:



The GH and KH test results are in number of drops required to achieve color change. Here's the secret decoder ring from their instructions:



My takeaways from this are that my RO filter system is working pretty well, and that the RPavlis water is significantly less hard than the "Perfect Coffee Water", but both meet the guidelines for use in the Micra. Agree? Disagree? Other thoughts? I know the general consensus is that RPavlis water will not cause scaling. Based on these test results, could the same be said for the "Perfect Coffee Water"?

Thanks!

I mentioned it before but since it's working so well and with zero negative effects...
After preparing my rpavlis water I make 5ml ice cubes, in the right proportion and ready to be used for one gallon of distilled water.

JohnPK wrote:I know the general consensus is that RPavlis water will not cause scaling. Based on these test results, could the same be said for the "Perfect Coffee Water"?

No, based on your results we can not say that PCW is non-scaling. They are not at all clear about the minerals in there, but based on what we think we know, i.e., that it appears to be an unknown mix of calcium chloride, magnesium chloride and sodium bicarbonate, at the GH:KH numbers you measured it would not be highly scale prone, but perhaps lightly scaling depending on how much of that hardness is from calcium rather than magnesium. The bigger concern here would be the chloride. At 4 drops (4°dGH) on an API test kit, that would be around 70 mg/L as CaCO3 of hardness minerals, and since that hardness is all from CaCl2 and MgCl2, that means around 50 mg/L of Chloride ion. I think the water spec for the LM Micra recommends 30 mg/L or less for corrosion risk reasons.

See also : Perfect Coffee Water

Thanks so much for all the information Pat. I'll stick to the RPavlis water for the Micra, and leave the PCW for pourovers and French press.

-John