Stop bath: citric acid or "regular"?

and as an ex-smoker for 18 years now, please don't smoke.

Wayne said:

Your post does not logically follow from mine. It happens in Ilford stop bath too. http://www.film-and-darkroom-user.org.uk/forum/showthread.php?t=10783 "I use Ilford Stop Bath diluted 1:19 (the regular version with the yellow indicator). It is stored at a reasonably low temperature, usually < 15 deg. C. I have found in the past that a jelly-like substance can form."

So don't buy Ilford (using your logic. You seem to have misunderstood my point). The point is there's no need for a biocide, even if someone has trouble with growth in citric acid its dirt cheap to dump and replace and plenty of people have no trouble at all.

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I have never used Ilford stop bath. I have used Kodak and several brands sold by FreeStyle, and I have never had a jelly-like substance.

FWIW, Ilfostop is citric-acid based.

Sirius Glass said:

In over six decades I have never had a problem with slime in stop bath.

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A couple of years ago I had a bottle of partially used working-strength (per the instructions) Kodak Indicator Stop Bath grow slime while stored in relatively benign conditions. I don't know exactly how old it was when that happened, or how depleted, but it was still yellow. When I asked PE about it privately he suggested adding 1 g/l Benzoic acid as a biocide. Rather than buying yet another chemical, I now mix and use stop bath single-shot. The stuff is cheap.

Doremus Scudder said:

FWIW, Ilfostop is citric-acid based.

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Um, yeah. That's the topic. Its probably the most widely used citric acid stop bath, has no biocide, and yet complaints about slime are pretty rare.

Wayne said:

What bacteria? Only certain people are having problems with slime. I don't know what the problems is in their cases but not everyone using plain citric acid stop has that problem. Clearly then, lack of noticeable growth is not proof of the presence of a biocide. However, absence of any growth in anyone's commercial SB would be strongly suggestive of one.

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There's something going on. I always have eyedropper bottles of 12% CA and 20% CA. Never noticed any kind of slime or growth and sometimes one or the other goes a few months before running out. An open tray is probably more susceptible to contamination than an eyedropper bottle, and maybe some places have different critters living in the air..like how sourdough bread tastes different depending on where it's made. My sodium sulfite gets stuff growing in it pretty quickly, even if I put it in a full sealed bottle...

Wayne said:

Um, yeah. That's the topic. Its probably the most widely used citric acid stop bath, has no biocide, and yet complaints about slime are pretty rare.

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How do you know it has no biocide?

I have a part bottle of Ilfostop that is ~20 years old and no slime. I much prefer the no smell over the Kodak.

I like the fact that if you do a search on the term "slime" from within Photrio, there are more than a dozen references to this thread, all at the top of the list.
If you leave water that has been exposed to the air, slime can grow in it, because bacteria growth happens. The amount of growth is highly dependent on the environment.
A concentrated stop bath - whether acetic acid or citric acid based - does not provide an environment that is particularly conducive to bacteria growth, although the lower concentration citric acid concentrate may be slightly more conducive than the higher concentration acetic acid concentrate.
If you dilute stop bath to working strength, the resulting environment is much more like water. Acetic acid in that water doesn't encourage bacteria growth as much as citric acid in water does. Or maybe it is that acetic acid in working strength stop bath discourages bacteria growth more than citric acid does. Either way, some people have problems with slime in citric acid based working strength stop bath when they don't have those problems with acetic acid based working strength stop bath.
And some people have problems with slime if they store any working strength stop bath.
I guess things like temperature and the quantity and type of bacteria present varies from person to person, just as people's slime risk tolerance varies.

Be careful Matt. Trying to act as honest-broker can have unintended consequences as I have found out in my Minimum Quantity of Perceptol thread.

Here's a short story to illustrate the point and introduce a bit of humour. In Scotland there has always been great rivalry between two football(soccer) teams whose supporters come from predominately Roman Catholic and Protestant backgrounds respectively. The teams are Celtic and Rangers

At one game a stranger with an English accent joins the crowd in the Rangers end. Rangers score a magnificent goal and he and the rest cheer wildly. Then Celtic do the same and the Englishman on his own cheers and applauds again. The Rangers supporters around him ask in anger what team he supports and he replies neither but he does recognise and support good football. The other supporters turn their backs on him, having discovered they have an atheist in their midst

pentaxuser

RattyMouse said:

How do you know it has no biocide?

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A deduction based on the fact that slime grows in it.

Interestingly, citric acid is often added to food to act as a preservative.

Ilford's literature says that Citric Acid should only be kept in its stock solution for 7 days. It's MSDS forms do not mention any addition other than citric acid and the dye. From doing a google search, I found that Citric Acid can also be used to make slime, which is apparently a very popular thing to do these days.

Like others, I have kept the solution much much longer than 7 days (3-4 months, I tend to replace my Stop when I replace my fixer) with no slime issues.

Wayne said:

A deduction based on the fact that slime grows in it.

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But you just said that complaints of slime are very rare. Which is it?

Wayne said:

do you get slime, or only use it once? Am I the only one who stores it without slime?


Edit: Oh, I just saw Barry's post above so I'm not alone.

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I mix it right before I use it so there's no slime. 1 tablespoon/liter of water. I also toss it after each print session. I use plain water for stopping film development.

RattyMouse said:

But you just said that complaints of slime are very rare. Which is it?

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Could be both. They are not mutually exclusive, although it seems unlikely Ilford would bother putting in an inneffectual amount of biocide.