Homemade sodium thiosulphate solution?

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skybloke

skybloke

Member
Apr 25, 2019
15
N. Bucks, UK
One for the chemists please! :)
A bottle of Taylor R-0007 reagent in the UK delivered is approx £15 for 60ml (2oz). That's nearly $20!
R-007 is a N/10 solution which (I'm no chemist) on investigation means 24.8g sodium thiosulphate(ST) per 1000ml or 2.48g per 100ml.
(Stop yawning at the back!)

You can buy ST crystals freely and very cheaply. Smallest 10g sample was £2 which would be enough for 400ml of solution = approx 7 of these Taylor 60ml bottles which would have cost (7x£15) = £105 as opposed to £2.

Am I missing something?.......a trick maybe?
 
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Depends on the quality of the sodium thiosulfate that’s being sold. Does the seller/manufacturer list a grade on it?

Typically in chemistry you’ll only ever want to use Reagent Grade chemicals because they are typically of very high purity and are standardized along with a certificate of conformance. There are even higher purity grades than “reagent” but those are typically only used in the most demanding of circumstances.

Give it a go and see what you get. It will likely work just fine as the R-0007 is only used to neutralize chlorine for the TA test.
 
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Thank you for your replies.

The product is listed as "Sodium ThioSulphate Pentahydrate 99% Photo Grade/Aquarium dechlorinator" so I think that would be good enough!

I deliberately didn't declare in my first post but I have ordered a Marine/Aquarium Alkalinity test kit that claims 100-200 tests for £9.50. It lists suitable for saltwater and freshwater aquariums and seems from the description like the identical Taylor reagents. It obviously didn't list Sodium Thiosulphate so hence my question as the Chlorine would need neutralising.
I don't know what the Taylor kit TA test costs in the US but here I'd pay about £29 ($37) for 250 TA count tablets giving me about 50 tests. So say $0.75/test. If my hunch regarding marine alkalinity tests works then on the conservative side it would work out at about $0.15/test = massive saving!
In preparing the ST solution I've read it would be best to boil the solution once made to kill bacteria that may be on the crystals/equipment. Do you feel it need some form of stabilising once made up?... or would it be good for a season (say) once dissolved, boiled and cooled. Any input is gratefully received.
 
Thought you may be interested Matt in how this turned out. I ordered the 10g sample of sodium thiosulphate. Dissolved 2.5g in 50ml distilled water and then topped to 100ml in a clean air-tight jar. Hope it stays stable for a while. Read something about adding a tiny amount of sodium carbonate but the chemistry was beyond me!

In keeping with the Taylor test I then added 2 drops to a 25ml pool sample.

That's as far as similarity goes because the aquarium kit test only uses a 4ml sample to which 2 drops of a reagent are added. It turns a jade green colour. You then add another KH reagent from a 1ml very thin syringe with minute graduations and (unlike Taylors where you count drops) wait for the colour change to red. At that point the remaining reagent in the syringe is read and the result calculated from a table. My result was 81ppm. This method is apparently more accurate and down to 5-6 ppm. For 200 tests per kit you use a 2ml sample, 1 drop of reagent and then double the reading. Accuracy will be 10-12ppm. The kit plus my own ST solution cost £10 ($13) and at 10-12ppm accuracy will do 200 tests i.e 5p ($0.06) per test.
For comparison the TA tablet count method sell a 250 bottle here about £27 delivered. To achieve a 10ppm measurement I'd be using 9 tablets per test - last test was 85ppm. So a bottle will do 27 tests at £1 per test.

That's 20 times more expensive! = No Contest.

The profit margin on the pool test chemicals is huge! We already knew that of course but this quantifies it quite well I think.
 
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The thiosulphate solution ought to be very shelf-stable. It can, occasionally, develop bacterial contamination as it acts as a nutrient solution but as long as you are careful with it and keep it sealed, it should be fine. If you notice any cloudiness to the solution, it should be discarded and remade.

No need for additives. If you add anything to the solution it could mess with the pH/TA of the test solution and you don’t want that. Thiosulphate is cheap so if it goes bad, just remake it.

Glad to hear you found a good alternate source.
 
JoyfulNoise said:
The thiosulphate solution ought to be very shelf-stable. It can, occasionally, develop bacterial contamination as it acts as a nutrient solution but as long as you are careful with it and keep it sealed, it should be fine. If you notice any cloudiness to the solution, it should be discarded and remade.

No need for additives. If you add anything to the solution it could mess with the pH/TA of the test solution and you don’t want that. Thiosulphate is cheap so if it goes bad, just remake it.

Glad to hear you found a good alternate source.
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Thought I'd update anyone interested (Matt?). I've used this method very successfully although it did require a fresh ST solution after a few months but this is pennies to do. I decided a while back to extend my search for affordable testing and looked at the CH test.

Currently a 250 tablet bottle costs me about £23 ( about $30) and at my current CH of around 300 will do 16 tests at £1.44/$1.88 per test. I came across a Calcium aquarium test using indicator powder and a Sodium Hydroxide titrant. The colour changes are very similar to Taylors but nowhere near the amount of titrant used and considerably cheaper. These kits are apparently also used by home brewing enthusiasts!

However, I kept getting a very low reading of around 125 mg/l (ppm). I was hoping for something around 300. So I spent a while investigating. It turns out these kits measure Calcium concentration (ions?) which is NOT the same as Calcium Hardness (Calcium Carbonate?) but there does exist a relationship between the two and that is to simply multiply the calcium concentration result by 2.5 to get hardness. .....and that worked a treat! £13 for 50 tests equals (£0.26/$0.33) per test about a sixth of the tablet count method. I've no idea what the Taylor CH reagents cost but I'll bet per test it's many many times more!

I hope that helps someone. 😊
 
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Sodium Thiosulfate is 158.11 g/mol (anhydrous) or 248.18 g/mol (pentahydrate).

For a 0.10N solution use 15.8 g/L (anhydrous) or 24.8 g/L (pentahydrate).

Use distilled water.
 
JamesW said:
Sodium Thiosulfate is 158.11 g/mol (anhydrous) or 248.18 g/mol (pentahydrate).

For a 0.10N solution use 15.8 g/L (anhydrous) or 24.8 g/L (pentahydrate).

Use distilled water.
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Thanks James but if you read post#1 you'll see I already have that information. This thread was started just to make people realise that there are other titration kits available should you not be able to get Taylor kits or simply find them too expensive.
 
@skybloke are you referring to the Salifert Calcium Profi-Test Kit? It's one of the tests I picked up while researching the various test kits and reagents available in the UK.

I have hard water and an indoor pool so evaporation tends to cause my CH to rise over time unless I drain and refill a bit. I am testing with the Taylor kit at the moment but will run out of R-0007 soon enough.
 

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jakeblat said:
@skybloke are you referring to the Salifert Calcium Profi-Test Kit? It's one of the tests I picked up while researching the various test kits and reagents available in the UK.

I have hard water and an indoor pool so evaporation tends to cause my CH to rise over time unless I drain and refill a bit. I am testing with the Taylor kit at the moment but will run out of R-0007 soon enough.
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Hi Jake thanks for replying.

Yes indeed I am talking about the Salifert kits which are cheap and very accurate for both TA and CH. If you follow my instructions above you should get great success. The water source is the deciding factor in how to handle your pool.

Like you I'm UK (water source CH = 250, TA =140) with an indoor pool. These are typical hard water values and, for me, is the limiting factor. I say that because years ago I ditched the stabilized tablets, after finding TFP, and moved over to CalHypo. So CH is important for me to monitor. I keep the TA down with Dry Acid. I do a 1/3 drain replacing with softened water when CH gets to approx 400 ppm which then puts the whole pool back to 260 ppm, which is the fill water value. I last did that in Nov '23 and I'm presently around 300 ppm so a long way to go yet. I have no problems achieving balanced water.
 
@PoolStored A couple of years ago they changed the law in the UK to require a licence to purchase various acids. To buy Muriatic acid here you have to have an EPP licence: Licensing for home users of poisons and explosive precursors

Dry Acid is basically the only realistic option here because "there are safer alternatives" in the eyes of the Home Office:
The licence application process will take you through a series of questions to check whether you need to apply for an EPP licence. It will prompt you to have all the necessary documents to hand, such as proof of identity and address.

On receipt of your application and payment, the Home Office will conduct checks into your suitability, including criminal record and health checks.

Offences that might be considered relevant to these checks are listed in due diligence checks.

Once a decision on your application has been reached, the Home Office will write to you. If accepted, a licence will be posted to you separately.

Applications are considered on a case by case basis; however, we generally do not grant licences where there are safer alternatives that would produce the same effect as the substance you are requesting. This includes substances for unblocking pipes or most other cleaning purposes. Unless there are exceptional circumstances, your application will likely be refused and you will not receive a refund.
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PoolStored said:
Dry acid adds sulfates to the pool water, which will corrode concrete and metals. I'd suggest that you switch to muriatic acid.

Acid - Further Reading

www.troublefreepool.com www.troublefreepool.com
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With respect, I've been using dry acid for controlling TA and pH for nearly 20 years now and have no damage to tiles, grout nor stainless metals. My TDS levels are low (presently at 400ppm). I also don't wish to handle liquid acids at that concentration. All my chemicals are manually deployed. This works just fine for me but thanks for your input.
 
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JamesW said:
TFP is a registered 501(c)3 non-profit that is maintained by user donations.

The people who answer questions are volunteers.

If you find the site to be a good resource, please consider making a donation to help support the site.

Thanks.

www.troublefreepool.com

Become a TFP Supporter

Help Support TFP Trouble Free Pool is run by a dedicated group of volunteers that … Read more…
www.troublefreepool.com www.troublefreepool.com
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Oh.... and I AM, most definitely, a supporter. By that I mean I pay annually for the app, which is world class!
 
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