Water pH question

[Terrence Brennan]

I made a post (like almost 12 years ago!!) about adding EDTA Disodium to the rather hard water I have with which to mix my chemicals. Whenever I mix developers, fixers or a hypo clearing agent, I get a percipitate in the bottom of the jug it is stored in; liquid concentrates are okay. Here is a link to my original post: https://www.photrio.com/forum/threads/disodium-edta.65227/

It would seem to me, as a non-chemist, that the water is excessively hard. A water softener is not an option, so I finally got off my posterior and bought myself a pH meter. I just calibrated it, with the recommended buffer solutions, and they gave the following readings:
Buffer 7.0 = 7.0;
Buffer 4.01= 4.1;
Buffer 10.01 = 10.0.

I also checked the tap water I use, which has a pH of 7.7, the distilled water has a pH of 5.4 and I mixed 400mL of tap water with 2.0g of EDTA Disodium, and got a pH reading of 4.7.

First big question, is my test with water a valid test? For if I am going to see a shift in the tap water of pH 3.0, it's going to require a massive overhaul of all of my developing times.

Second question, what chemicals would be required to make the appropriate pH shift? I mix D-23, F-7 and the hypo clearing agent in "The Darkroom Cookbook," which is basically a 2% sodium sulfite solution and a 0.5% sodium bisulfite solution.

All inputs from those who are well versed in the chemical persuasion will be gratefully received!

 

[runswithsizzers]

My limited experience with a few hobbiest-grade pH meters indicates that getting a reliable calibration can be frustrating. Did you do a one-point calibration - or...?

This article discusses why it is harder to get an accurate reading with deionized water, compared to tap water: https://camblab.info/testing-the-ph-of-distilled-water/

Depending on the buffering capability of your final solution, the initial pH of the water you used to make that solution may not be all that important (?)

 

[Terrence Brennan]

My limited experience with a few hobbiest-grade pH meters indicates that getting a reliable calibration can be frustrating. Did you do a one-point calibration - or...?

This article discusses why it is harder to get an accurate reading with deionized water, compared to tap water: https://camblab.info/testing-the-ph-of-distilled-water/

Depending on the buffering capability of your final solution, the initial pH of the water you used to make that solution may not be all that important (?)

Thanks for the reply. I did a three point calibration, and then mixed 400mL of D-23, with and without the EDTA Disodium. I found that the D-23 without EDTA Disodium had a pH of 7.9, and the D-23 with EDTA Disodium had a pH of 7.7. I would hazard a guess that the 100g/L of sodium sulfite, which acts not only as a preservatrive but also as an accelerator, might account for the fact that two developers are fairly close in Ph. It could also mean I made an error in my initial readings, but I like to think not!

It remains to be seen what effect this will have on development times; I am going to make a couple of step wedges on Eastman Double-X Negative 5222, using what I laughingly refer to as my "pulsed xenon lightsource." It is, in fact, an Omega B-22-XL enlarger, with the regular lamphouse replaced with a home-made contraption, using a small electronic flash as a source. A typical exposure or DXN is 1 "pop" @f/8, through Wratten 2B, 81A and ND 1.00 filters.

But as always, one can make as many tests as one wants to...but the proof is in the printing!

 

[runswithsizzers]

How much confidence do you have in your pH meter to resolve tenths? In other words, if your meter has precision of +/- 0.2 pH, then your two readings are not just “fairly close” they are the same. But if your meter can read +/- 0.02 pH, then you can trust the difference in the tenths position.

Is there some target range of pH which is recommended for your D-23?

 

[koraks]

For if I am going to see a shift in the tap water of pH 3.0, it's going to require a massive overhaul of all of my developing times.

Water (tap, distilled etc) has no buffering capacity whatsoever. pH readings that would nominally be 7.0 will be thrown off by a massive degree by even the tiniest impurities. All this resolves itself if you mix developer, which tends to be quite strongly buffered due to the use of stuff like carbonate and sulfite.

So don't fuss about the pH of your water. Unless you draw it directly from a peat bog (and even then...), it won't affect developer activity.

 

[Alan Johnson]

It's easier to forget about EDTA addition [I have some] and just let the precipitate [mostly calcium sulfite solubility only 43 mg/L cf hard water about 200 mg/L calcium carbonate] settle.
Then filter the nearly clear solution through cotton wool.