Weekly Shock

[Haywire]

Seems I read someplace that when on the dichlor/bleach method, that you need to shock the spa to 10ppm FC once a week. In the 3-4 weeks that I've been on this method, I've been keeping it at 1-4ppm with no weekly shock. It seems the water isn't quite as crystal as it was and the bubbles from the jets don't break up quite as quickly as they once did. Could not shocking once a week be the cause?

Ian

[chem geek]

It's with Nature2/MPS that you usually need to shock with chlorine once a week or so. With Dichlor-then-bleach if you are adding enough chlorine after each soak then you shouldn't need to shock at all. When you say you have been keeping the chlorine at 1-4 ppm FC, what do you mean? Do you mean that is your target right before your soak so you are adding whatever chlorine is needed after your soak so you get that much for the next soak and if you aren't soaking right away you add chlorine in between to maintain it at this level?

The reason I ask is that the amount of chlorine you add after a soak can have the FC get a lot higher than 4 ppm depending on how long you soaked and how many people were in the tub. It sounds to me like maybe you aren't adding enough chlorine after the soak so the FC gets too low or maybe even to 0 at some point and that you're getting behind in oxidizing your bather waste.

How many people soak and for how long? How much chlorine are you adding after each soak? Do you have an ozonator? Are you comparing the water quality relative to when you are on Baquacil?

[Haywire]

I check the FC and pH every day when I get home and add enough bleach to bump it to 4-6ppm. It's usually about 0.5 - 1.0 ppm when I check it (Taylor drop test). I don't specifically add it just before or after a soak. My wife usually soaks 20 minutes in the morning and evening, and about half the time, I join her in the evening. No bathing suits. PH is usually around 7.6. TA is 65. CYA is at 30. This morning after our 20 min soak, I bumped it up to 8 ppm.

Ian

[chem geek]

Do you have an ozonator? How many gallons are in your spa?

So if it's at 0.5-1.0 when you check it, you may not be adding enough after your soak and you should be adding it right after every soak. Otherwise, the chlorine may be close to zero after your soak for too many hours and that lets bacteria grow and even if the chlorine isn't at zero but is low, then the ammonia and organics from your sweat and urine will build up and can make the water dull/cloudy. Some of the components of sweat and urine are slower to oxidize so need the entire time from after your soak until before your next soak the next day (or certainly 10-12 hours) to get rid of and it needs a full blast of chlorine to do this.

A 20 minute soak for one of you would need around 10 teaspoons of 6% bleach, but in 350 gallons that would be around 2.3 ppm FC while two of you soaking would be double this. The FC isn't your target -- you don't try and target and FC after your soak. You instead add an absolute amount of chlorine proportional to your bather load and you only adjust that based on whether the FC at the start of your next soak is around 1-2 ppm FC.

Since you added more chlorine after the soak this morning, see what that does. If the chlorine level has still dropped to a low level tonight, then you've gotten behind your bather load and may need to shock to catch up. If only one of you soaked this morning, then the FC should be around 3-5 ppm FC tonight before your soak which is higher than you need. If both of you soaked this morning, then the FC should be around 2-3 ppm. Let us know what you measured tonight.

[Haywire]

No ozonator, 325 gallons. It did seem a little clearer last night after the extra chlorine. I'll change my routine.

Thanks,

Ian