Any meaningful difference between washing soda and soda ash?

Hi all,
Had occasion to set up my electrolytic deruster again today (commonly known as a benchtop 12V power supply, a big Rubbermaid tote, and an old piece of sprinkler pipe bodged together with some wire and alligator clips) and I noticed that I'd apparently used it enough that my supply of washing soda was getting low. I don't remember where I purchased it last time but I don't remember it being unusually hard to find. Well, after hitting two grocery stores and several chain hardware stores, I was starting to get a bad feeling. Arm and Hammer's web site was useless as they don't show any local retailers to me and their "contact us" form doesn't seem to actually work.
So I stopped by a local pool service place and the guy was happy to sell me a quantity of soda ash but I'd have to bring my own container as they only stock it in large bags (although depending on price I'd be happy to buy one of those as well.)
Question is, I know that they are both ostensibly sodium carbonate. Is there any meaningful difference in washing soda intended for use as a detergent ingredient (in case I'd want to use it for same) and soda ash used as a pH balancer for swimming pools, e.g. additives, allowable levels of impurities, other? Or is it really just two different names for the same thing?
I'm definitely going back to the pool supply but wondering if I should get a small container or just grab a 5 gal. bucket and get a lifetime (or at least a decade's worth) supply.
nate
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On 3/28/2013 4:45 PM, Nate Nagel wrote:

They should be the same but purities may be different. Sodium carbonate is a cheap chemical. In ton quantities it costs about 10 cents a pound.
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Nate Nagel wrote:

Sodium carbonate Na2CO3 is known as soda ash or washing soda, so in that sense it is two different names for the same thing.
But...
Sodium carbonate is not what I use in my pool to adjust total alkalinity. I do that with sodium bicarbonate or baking soda which is NaHCO3.
The washing soda is a classical water softener. However, some people use baking soda as an adjunct to washing.
My swimming pool supply place sells baking soda in 50# bags, but I get a better price and a more convenient packaging by buying Arm & Hammer at Costco in 13.5 lb. bags.
I have never purchased soda ash/ washing soda/ sodium carbonate in any quantity for any purpose.
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Mike Easter

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Is

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He didn't say sodium carbonate was used to adjust total alkalinity in a pool. He said it's used to adjust PH, which is 100% true.

Then you aren't following standard pool practices. Just look at any of the containers of PH decreaser in a pool store. They are all sodium carbonate.
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On 03/28/13 04:45 pm, Nate Nagel wrote:

IIRC, soda ash might be anhydrous, whereas washing soda is likely to be a crystalline form containing a lot of water. You might be able to compare their relative efficiency if both have detailed specs. on the packages.
Perce
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On 3/28/2013 4:45 PM, Nate Nagel wrote:

I used soda ash from pool suppliers for dyeing fabric. The dye seller advised buying from pool supplier to save shipping, although the dye seller also sold it. I think "washing soda" is just a popular name for the same stuff. IIRC, I purchased it in 5# buckets.
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