Re Ammonia \ Chloramine \ Chlorine

[coolie]

Re Ammonia \ Chloramine \ Chlorine, can anyone help me do the math and chemistry based on a report from my water authority?

My water authority tells me they don't publish figures for the amount of chloramine in tap water, but they do the amount of free chlorine, total chlorine and ammonia from which chloramine can be worked out.

Seem strange I know, but that's what they have said.

To make matters worse, the last few water changes, I have been letting two big buckets of water stand for 24 hours to let chlorine escape, thus only having to remove chloramine, (some of which has also dissipated by that time but disregard that) all in order so I can use half the amount of Sodium Thiosulphate (in order to remove the left over chloramines only) and lower the need to put Sodium in the tank.

So...

These are the figures for my area : Chlorine Free (mg Cl2/l) 0.028
Chlorine Total (mgCl2/l) 0.224
Ammonium (mg NH4/l) 0.039

So can anyone help me work out the Chloramine total after these figures, and how many mg of Sodium Thiosulphate are needed to dissolve just the Chloramine only after leaving standing for 24 hours based on the following guide found on the internet: "dechlorination of 10 litres of standard tap water at 4ppm chlorine content, between 0.1g and 0.2g of Sodium Thiosulphate is required"

Any help or errors on my part appreciated.

 

[DrRob]

So you've got about 2 mmol of ammonium per litre. Chloramine has a 1:1 ratio and the chloride weighs about 35.453 (so there's 6 mmol of total and 0.8 mmol of free).

Likelihood is that you've got around 2 mmol per litre of chloramine and the rest of the bound chlorine is probably bound in various organics or a few other salts.

 

[coolie]

Thanks DrRob, did you nick my neon tetra avater from a different site (username Fish?), anyway, I kind of follow you, it seems my guess to use half the amount of thiosulphate 24 hours after standing water has been WAY-OUT and free chlorine is tiny in comparison to chloramine?

 

[DrRob]

It's a glowlight tetra.

 

[coolie]

sorry for the confusion there DrRob, I can't even blame that on my colorblindness.


Now, provided that mg/l works out the same as ppm, the quote "dechlorination of 10 litres of standard tap water at 4ppm chlorine content, between 0.1g and 0.2g of Sodium Thiosulphate is required"
seems to be a bit out.
The figures from my water board are saying: Chlorine Total (mgCl2/l) 0.224. Am I missing something here? That's 0.224 mg of Cl2 per litre or 0.224 parts per million,
which means I will need almost half what that quote is proposing?