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Sodium Hypochlorite strength

I recently took over for a system and are having issues with the chlorine.

I suspect our 12% chlorine solution is weak. We are pumping out of a 55 gal. drum but are only using 4-8 gals. per month with a automatic refill each month from our supplier.
How can I check for strength using my Hach colorimeter II? What is the dilution rate and formula?

Also We are having a problem with real low Free chlorine readings 0.4 - 0.7 and high Total readings 1.8 -3.0 mg/L at the same sample?
I am assuming that either there is a problem with the chlorine strength or there is something that is interfering with the dpd tests?
I have checked for free ammonia and have a result of 1.85 mg/L? I have not been able to find much info on the corrilation but was suggested to check to see if high ammonia? Not sure if this is high or not? or what it may indicate?

Any help or suggestions would be greatly appreciated!

Re: Sodium Hypochlorite strength

At a normal pH of 6-8 SU sodium hypochlorite can degrade substantially in 2-3 weeks. It may be stabilized by raising the pH with sodium hydroxide. The pH needs to raise to 11 SU in order to stabilize the sodium hypochlorite.

From what information you are providing, it is likely a problem with topping off the 50 gallon container every month with a relatively low volume of new product. I suspect your solution is not near the 12% you think it is. You could get a fresh 1/2 month supply of sodium hypochlorite and keep it separate from your other product and try feeding it and see if it provides better results over a few weeks. If it does that is your sign. You are purchasing new frequently anyway so that would be an easy experiment. If it works you can either continue small volume purchases every couple of weeks instead of monthly which it appears you do now or jar test with the sodium hydroxide to find the right mixture for a pH of 11 and stabilize your new product that way.

I have used sodium hypochlorite in wastewater for filament control and we could definitely see that it degraded quickly when held over a few weeks. Degradation may be a problem for you.

Chlorine is also very reactive and it could be effected by various reducing compounds and nitrogenous matter and may react with organic matter to produce chlororganic compounds or other combined forms of chlorine which have slight disinfecting action.

Re: Sodium Hypochlorite strength

thanks Steve for the reply,

At this point we've decided to use as much as we can from what we have currently then when the residuals drop off were set to switch to a smaller container so we will use at least 50-70% of container before refilling within 1 month - 6 weeks.