SODIUM THIOSULPHATE

[fisherman]

At the present I am using activated carbon not cheap to buy I have been looking to use SODIUM THIOSULPHATE as it is far cheaper to use than carbon •To dechlorinate tap water for aquariums or treat effluent from waste water treatments prior to release into rivers. The reduction reaction is analogous to the iodine reduction reaction. Treatment of tap water requires between 0.1 grams and 0.3 grams of pentahydrated (crystalline) sodium thiosulphate per 10 liters of water.
What are your views on using SODIUM THIOSULPHATE to DEchlorinate your water

[Duncan]

hi peter

The dose depends on the amount of chorine and chloramines in the water supply as its illegal in the uk to put more than 0.5ppm in the supply you can actually get away with a very small dose
The up side is as you say its cheap and does the job very effectively.. the down side is it puts sodium into the system this raises your TDS also it frees up ammonia from the chloramine as you know ammonia and chlorine makes choramine by neutralizing the chorine side of the molecule you free up the ammonia molecule that was previously lock to the chlorine

the down side of carbon is the cost as you say, you have to flow water through it at the right rate( to fast and you dont take out chlorine) and you don't really know when its used up!

dunc

[Manky Sanke]

At the present I am using activated carbon not cheap to buy I have been looking to use SODIUM THIOSULPHATE as it is far cheaper to use than carbon •To dechlorinate tap water for aquariums or treat effluent from waste water treatments prior to release into rivers. The reduction reaction is analogous to the iodine reduction reaction. Treatment of tap water requires between 0.1 grams and 0.3 grams of pentahydrated (crystalline) sodium thiosulphate per 10 liters of water.
What are your views on using SODIUM THIOSULPHATE to DEchlorinate your water

That amount appears to have come from an aquarium website. Adding a set amount of sodium thiosulphate per 10 litres may be suitable when topping up an aquarium but isn't very exact when you scale it up to the amounts you would need when topping up a pond. Adding 0.3 grams per 10 litres equates to 30 grams per 1,000 litres or 137 grams per 1,000 Imperial gallons which is ten times higher than necessary to remove chlorine or chloramine.

A dose rate of 13 gm per 1,000 gallons of new water added (not pond volume) will dechlorinate water up to a supply level of up to 0.8 mg/L which provides a 50% safety margin above the chlorine level that’s normally allowed in case the supply authority adds any extra “to sanitise the supply network” after a burst main or planned work.

It’s ok to use this amount without a risk to koi because, although there is no research that I can find for the toxicity of sodium thiosulphate on carp, the toxic threshold for other, more delicate, fish species is between 10,000 mg/L - 24,000 mg/L. This equates to in excess of 45 kg per 1,000 gallons so 13 gm per 1,000 gallons is 3,000 to 8,000 times lower than the toxic level.

Adding sodium thiosulphate to a pond will increase the TDS value because adding anything that is (or was) a solid will obviously increase the amount of Total Dissolved Solids in it. Even when it combines with chlorine, it won't make the chlorine vanish. Sodium thiosulphate combines with chlorine to make a small amount of salt plus some harmless left over sulphur, which, as Duncan says, will increase the sodium level because the salt then dissociates (chemically splits up) into sodium and chloride.

Where there is chloramine in the supply, sodium thiosulphate combines with it to make the same amount of salt and sulphur but the ammonia in the chloramine will be released. For normal top ups this will be a small additional amount of ammonia that a properly working biofilter will soon remove. For larger changes, the amount of ammonia released will depend on individual situations so it would be advisable to check the ammonia level with smaller changes, such as 10%. This will allow an assessment of the level of ammonia released before using sodium thiosulphate for larger water changes.

If you want to use sodium thiosulphate, there are two forms commonly on sale. The most common form is sodium thiosulphate pentahydrate (sometimes called hypo by photographers) which is the white or pale pink crystalline form and is the best one to use. Dissolve it in water and sprinkle around the pond in the usual way before adding the new water.

Sometimes sellers give the chemical formula instead of describing it as sodium thiosulphate pentahydrate. If you see this formula Na2S2O3 . 5H2O it's the right one. Don't worry about trying to remember it, as long as it ends in 5H2O (five molecules of water) it's the right one.

[Duncan]

thanks for that Syd

I was not going to say it peter but I sell 250 gm of S/T and that makes 2 litres of solution use this at 10ml to every 100 gallons being replaced
its more than enough for british needs when dechlorinating
dunc

[Manky Sanke]

For those who want to use sodium thiosulphate, it would be a good idea good idea to get your supplies from Duncan. The crystals he supplies are of high purity. There are many other suppliers but the purity isn't always guaranteed either in the original manufacturing process or it may have been transported or stored in containers that have previously been used for other chemicals. For most uses, a slight reduction in purity isn't a problem but, where fish are concerned, I wouldn't take chances.

For anyone who doesn't "do" maths and hasn't spotted it, dissolving Duncan's 250 gm into two litres of water as a stock solution and using that at 10 ml per 100 gallons of top up water being added equates to a dose rate of 12.5 gm per 1,000 gallons which is a hair splitting difference from the 13 gm per 1,000 gallons that I mentioned above and which has a 50% safety margin anyway.

[fisherman]

Duncan
There’s nothing like blowing your own nose once my carbon filter needs toping up I will get some Sodium Thiosulphate from you
Regards Pete