Ph level of water from faucet and RO system

[Steven Ruttenberg]

Faucet it is 7.56 from RO it is 6.46. Kinda large swing. Faucet is base and RO is acidic. Hmmm

[Steven Ruttenberg]

My Kodak stop bath mixed with RO water is 2.56.

[Peter Collins]

Steve, why is your RO water NOT pH 7? If it is high-megaOhm water, it should be 7. 18 megaOhm RO water is used by env. labs using EPA test methods. Required. I know, I worked in one. High megaOhm means it has nothing in it to affect specific conductance.

Now, for something completely different: developer, stop bath, and fixer pH likely not a significant variable. Processing time, developer solution temperature (AND temperature change DURING development if times are 8 min plus) more significant. Stop is stop and fixer is just, well, fixer.

[Steven Ruttenberg]

I don’t know why the RO is slightly acidic All I can think of is filters are 2.3 years old.

[koraks]

developer, stop bath, and fixer pH likely not a significant variable.

Developer pH is, within certain margins, very significant. A +/-0.1 difference isn't likely to have much effect, but a +/- 0.5 or greater difference can produce problems. With commercially packaged developers, I personally always assume that they are sufficiently buffered and formulated in such a way that they are fairly insensitive to differences in the water supply. This, however, is certainly not the case with home-brew formulas. I use these a lot and I find that establishing the correct pH is essential in some cases. For example, instant Mytol (DIY XTOL alternative) formulas give me (YMMV) way too low pH when mixed according to the published formulas and I need to adjust them to the correct pH of 8.2. The same with the Bonavolta C41 formula which I use a lot and which gives again a way too low pH if the recipe is followed, and it needs to be adjusted upward to get correct gamma and color balance. Evidently, pH is more important with color than with B&W, but it proved to be enough of an issue with the Mytol example to produce unprintable negatives without adjustments.

pH of stop and fix are indeed of lesser importance and there is significant leeway in those cases (except for color work, where the pH of the fixer really should not be below 6.5 to prevent leuco dye formation).

[Leigh]

What's RO ? ? ?

- Leigh

[djdister]

What's RO ? ? ?

- Leigh

Reverse Osmosis filter.

[Leigh]

Reverse Osmosis filter.

Why would that change the pH?

I thought it meant Ruthenium Oxide.

- Leigh

[djdister]

Why would that change the pH?

I thought it meant Ruthenium Oxide.

- Leigh

From the interweb:

Reverse osmosis water purifiers will reduce the pH of drinking water. Because reverse osmosis removes the minerals in water the water will then react with carbon dioxide upon exposure to air to form carbolic acids, thus lowering the pH.

[Leigh]

From the interweb:

Reverse osmosis water purifiers will reduce the pH of drinking water. Because reverse osmosis removes the minerals in water the water will then react with carbon dioxide upon exposure to air to form carbolic acids, thus lowering the pH.

OK.

If that's a known effect, I don't understand why the OP asked about it.

- Leigh