Sodium Thiosulfate

Someone just PM'd me:
Kathy, 
Could I ask where to buy Sodium Thiosulfate and how do make up a stock solution to add to my 2 liter phytoplankton culture. 
Thank you so much, 
xxxx
 
I appreciate the question, and thought the rest of those folks with the same question would like to have the answer as well.
 
There are a number of sources of Sodium Thiosulfate, google is your friend here, but I got mine from Florida Aqua Farms, in 2006, a lifetime supply.  Get yourself a postal scale from Office Depot or Max, and weigh out 6 grams of ST, dissolve in 100 ml of water, salt or fresh, but not tap (chlorine in there).  This is your stock solution.
Now if you have used 2 ml of bleach to sterilize 2 gallons of water, just use 2 ml of ST to dechlorinate.
 
Household bleach is about 5.5 % chlorine, one gram of ST neutralizes one gram of chlorine, so using an equal volume of 6% (6 grams in 100 ml water) ST should make sure that you are chlorine free.  I always test with a chlorine test strip anyway, just to be certain.

check out Kathy's Clowns, llc website:
http://kathysclowns.com
Captive bred clownfish and more
(Wholesale to the trade.)

It is important to note that certain brands of household bleach have recently increased the concentration of sodium hypochlorite in order to make the product more concentrated to save on shipping cost.  For example, I have a bottle of Clorox brand bleach in my fish room with a concentration of 8.25%.  The amount of sodium thiosulfate needed to ensure dechlorination should be increased proportionally (e.g., 8.25/5.5 = a factor of 1.5) when using such stronger bleach.

In that case, would I use 8.25 grams per 100ml of water to make it a 1/1 ratio to neutralize it?  I know its a simple question but wanted to make sure I understand it right before I start "experimenting" lol.

Short answer:  Sure.
 
Long answer:  The formula given above errs on the conservative side, i.e., it actually has more sodium thiosulfate than is necessary to get the job done, as a safety factor.  The balanced equation for the reaction is this:
 
4 NaClO + Na2S2O3 + 2 NaOH → 4 NaCl + 2 Na2SO4 + H2O
 
In simple English, this means that you need 1 sodium thiosulfate molecule to neutralize 4 sodium hypochlorite molecules.  The molar mass of sodium hypochlorite is 74.442, and the molar mass of sodium thiosulfate pentahydrate (the crystal form we use) is 248.18.  So, that means that for every 1 gram of sodium hypochlorite we need to neutralize, we need (248.18 / 4) / 74.442 = 0.8335 grams of sodium thiosulfate pentahydrate crystals.
 
For the 8.5% bleach example given above, that would mean 8.5 * 0.8335 = appx. 7 grams per 100 mL would be the correct amount of sodium thiosulfate for a 1:1 ratio, however, conventional wisdom is to bump that up a bit for safety's sake.  Simply removing the "* 0.8335" part will give a solution that is about 1.2 times stronger than is necessary, which is a nice, conservative safety factor.
 
Simply put, if you make the sodium thiosulfate pentahydrate solution the exact same concentration as your bleach solution, and use it at a 1:1 ratio, you will have a dechlor solution that has a 20% margin of safety built in.  At the concentrations we are using to bleach, the extra thiosulfate should not be a concern.
 

Thank you both for this great thread!  Lots of good info I'll be using.

I find RGcomplete to be very convenient, easy, and effective to use for growing Brachionus rotifers.  

http://www.bbk.ac.uk/
http://www.microsoft.com/
http://www.mybraindumps.net/MCSA-SQL-Server-2012-guide.html
http://www.berkeley.edu/index.html