For the chemist types… can you explain?

[James Phillips]

I was in a store today with a friend who was buying chemicals for his home spa. Curiosity took over and I began to look around and read the labels. On the shelf were two identical looking containers with one stating that is was a Ph + product (increases the ph value of the water) while the other said it was a Ph – product (decreases the ph value of the water). I started thinking that these might be useful in a darkroom especially since the price was ridiculously low for the volume offered.

I turned them over and read the labels. Both products would only claim to have sodium bisulphate in the container.

My question is “How can these products provide both Ph increase as well as Ph decrease from the same chemical (i.e. sodium bisulphate)?

I am sure that the products work as stated it is just that I would appreciate a small Chemistry 101 lesson on this topic.

Kind Regards,

[Steve Baggett]

I don't see how they could be the same product. In my pool (and spa chemicals are generally the same), to increase PH (make more alkaline) you add soda ash. To decrease PH (make more acidic) you add muriatic acid crystals. They are in distinctly labeled containers. Can it be that the "placebo effect" works also on pools and spas and the ingredients are actually inert? :))

[Nick_3536]

I think the sodium bisulfate will be Ph down or Ph -. The pH up I have is sodium carbonate. Considering what our tap water is like I'm not sure why anybody would need to add more carbonate.

[Jorge Gasteazoro]

It cant be, sodium bisulfite will oxidize into sulfuric acid.

[Tim Curry]

I use "pool chemical" sodium thiosulfate or "neutralizer" as it is sold in swimming pool supply stores. It's been a while since I bought some, but I think it was about $40 (US) for a 25 pound pail of the stuff, also available in 50 pound bags. It is commonly known as "hypo" in the lab and works well for fiber based papers, cheap too. You may need to get them to look up the actual name in their MSDS files to be sure of the chemistry.

[Mark_3632]

TO bring PH levels down in my Classroom hydroponics garden I use a 9% solution of phosphoric acid (check your coke can it is in there too. Any sodium would increase the PH according to my books. What would you use it for in the darkroom? I'm curious now.

[David Karp]

There is a product called PH+ for use in pools that Patrick Gainer says is anhydrous sodium carbonate. I have some in my darkroom, intending to mix up some D-72 and other elixers, but have not gotten around to it yet. If it is the same product, then yes, there is some value for use in the darkroom.

You can check out Pat Gainer's article at http://unblinkingeye.com/Articles/VitC/vitc.html.

[Wayne]

Bisulphate is definitely Ph- down. I used to use it in divided developers.

[Julio Fernandez]

James: Please read the labels again and this time carefully. You have two different chemicals: One is Sodium BisulFATE which lowers pH (it is very acidic). The other is Sodium BisulFIDE and it should increase pH as this material hydrolizes to yield Sodium Hydroxide which is very alkaline.