Normal to smell bleach while using trichlor?

[ITR]

Okay, so I started using trichlor this summer. My mother comes down in the winter time and helps manage the pool when I have to travel...but in the summertime she is back in Iowa, so I decided to use the auto chlorinator (inline) since my CYA is at 40 and I didn't want algae while I was gone. The last two months I have notice a chlorine smell when the pump comes on. It subsides after about 30 minutes and my CC is never higher than .5...generally it is at 0.0.

Is this normal? I never smelled it when using bleach.


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[Donldson]

I think the main issue is the water that sits in your feeder while the pump is off. The pH will drop very low while the FC will rise considerably. When you turn the pump on the first water that shoots out of your return is heavily chlorinated and very acidic, a surefire way to create a strong chlorine smell. You should be able to minimize the problem if you run your system in multiple short bouts instead of one long one. For example, if your timer will allow it and you run 8 hours a day then running for 2 hours 4 times a day should reduce this problem quite a bit. It might be worth looking in to a stenner pump or SWG to fully automate without dealing with trichlor.

 

[ITR]

That's a good idea...I'll set a few small cycles. Right now I only run the pump an hour a day on high and another hour on low., but I can certainly program more cycles. Thanks!

The better half is against SWG, although I am trying to wear her down...I mean helping her understand the salt won't be an issue with her RA. I did get a quote on a sterner pump install and chemlink but at $3500 installed that will have to wait a season.


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[tim5055]

I did get a quote on a sterner pump install and chemlink but at $3500 installed that will have to wait a season.

if it were me I would go with the SWCG or Stenner, but stay away from any automated testing controls,like the ChemLink. The sensors are just not good enough or stay in calibration long enough to give me a warm comfortable feeling that everything is being added properly. I recall a recent post where their auto dispense for acid went out of wack and added the entire tank (several gallons IIRC) of muratic acid to the pool all at once.

 

[chem geek]

If there is no water flow, then Trichlor produces very high FC and low pH water near the puck and those conditions lead to some breakdown of the chlorine in to chlorate and some oxygen gas and also can produce some nitrogen trichloride which is very smelly, volatile, and irritating. It, along with dichloramine, is what is associated with "bad pool smell". It only takes 0.02 ppm to be noticeable so won't generally show up in a Combined Chlorine (CC) test. So if what you were smelling was like "bad pool smell" then it might have been this nitrogen trichloride. If it was more of a "clean bleach" smell, then it was more likely to be the concentrated chlorine which when the pump first turns on can result in more outgassing of chlorine so be more noticeable.

 

[ITR]

Got it. That all makes sense. Thanks chemgeek!

As for the controls...a stenner pump alone for bleach will do nothing for the HCL, right? Or am I missing something?

I need to make sure the pH doesn't rise on me too while I am gone...hence why I thought trichlor would be the best option since it is a bit acidic and will help with the pH rise. If there is another way to control FC and pH when gone for two weeks at a time, I'm all ears....


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[jmastron]

Got it. That all makes sense. Thanks chemgeek!

As for the controls...a stenner pump alone for bleach will do nothing for the HCL, right? Or am I missing something?

I need to make sure the pH doesn't rise on me too while I am gone...hence why I thought trichlor would be the best option since it is a bit acidic and will help with the pH rise. If there is another way to control FC and pH when gone for two weeks at a time, I'm all ears....


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I don't have a SWCG yet, but my understanding from posts here is that if you can lower the Total Alkalinity, the pH won't rise as fast. Without a SWCG, my pool takes 2+ weeks to rise from 7.2 to 7.8; I don't know how much faster to expect with a SWCG. How fast was your rise when you were using bleach?

 

[chem geek]

A stenner pump for chlorine doesn't control the pH, but the increase in pH from chlorine addition should be balanced by the decrease in pH from chlorine usage/consumption. Basically when using hypochlorite sources of chlorine it is close to net pH neutral except for the small amount of excess lye, but you should not notice that in only 2 weeks. This means that if you are seeing pH rise, it is from other sources such as carbon dioxide outgassing because your TA is too high or you've got other sources such as new plaster. If you use a pool cover, that should eliminate the outgassing.

 

[ITR]

I don't have a SWCG yet, but my understanding from posts here is that if you can lower the Total Alkalinity, the pH won't rise as fast. Without a SWCG, my pool takes 2+ weeks to rise from 7.2 to 7.8; I don't know how much faster to expect with a SWCG. How fast was your rise when you were using bleach?

It's a newer pool (about eight months old) so it raised pretty quickly. I think I am down to needing about a gallon of HCL a month (which is nice given I remember when I was going through two gallons a WEEK). It rises about .4 or .5 a week with trichlor. Afraid to go back, but I'll be around for the next two weeks so I might go back and give it a try.

- - - Updated - - -

A stenner pump for chlorine doesn't control the pH, but the increase in pH from chlorine addition should be balanced by the decrease in pH from chlorine usage/consumption. Basically when using hypochlorite sources of chlorine it is close to net pH neutral except for the small amount of excess lye, but you should notice that in only 2 weeks. This means that if you are seeing pH rise, it is from other sources such as carbon dioxide outgassing because your TA is too high or you've got other sources such as new plaster. If you use a pool cover, that should eliminate the outgassing.

My TA is at 60...which seems to be where the pool likes it. Lower than the target range, but it does help keep the pH down. I assume the pH rise is from the plaster curing...which is definitely getting better. Eight months in and the pH rise is slowing down. Thanks for the help...I'll have to shutoff the autochlorinator for a few weeks and see how it goes.