When To Shock

[sl3238]

Have my Tub open for about 10 days and all my numbers have been pretty good....When should i shock treat and how often??? Currently, i"m using chlorine to maintain and have a product called "Fresh 'N Clear ( From Leslie"s Pool) for the shock..

[bart6453]

Have my Tub open for about 10 days and all my numbers have been pretty good....When should i shock treat and how often??? Currently, i"m using chlorine to maintain and have a product called "Fresh 'N Clear ( From Leslie"s Pool) for the shock..

Shock your tub when your combined chlorine exceeds .5ppm

At least that's what I do.

[NewB@Spa]

I too also wondered what the breakpoint was for "shocking". I wasn't comfortable with shocking just for the sake of maintaining a schedule. Currently (almost a week into new fill) I am Ph 7.8 (just added Ph down), FC 5, CC .5

I haven't remeasured my TA (should I?). By calculated method I have approximately 15 CYA. I guess it will take another week or so to accumulate 25?

[bart6453]

I too also wondered what the breakpoint was for "shocking". I wasn't comfortable with shocking just for the sake of maintaining a schedule. Currently (almost a week into new fill) I am Ph 7.8 (just added Ph down), FC 5, CC .5

I haven't remeasured my TA (should I?). By calculated method I have approximately 15 CYA. I guess it will take another week or so to accumulate 25?

I would test my TA just to know where it is at. In function, I have found that while good information to know, my PH swing is more indicative of whether my TA is too high or too low. If my TA is too high my PH tends to rise, if my TA is too low my PH tends to lower, once my TA is right on the PH seems to lock and stays there for literally months at a time. As you add PH down, your TA will also decrease.

As to your CYA, for every dichlor adds 9ppm CYA for every 10ppm FC. For me it usually takes about 2 weeks to achieve 25pm CYA. I found it very easy to pre-measure the amount of dichlor I need to add to get to 25ppm CYA. Then just add from the measured amount until it's gone, when gone I switch to bleach.

I highly recommend using the pool calculator and the ipod/iphone pool calculator application.

[NewB@Spa]

Tested last night and it had dipped to ~50ppm. Added Baking Soda per Pool Calculator. Hopefully everything evens out. SO far so good nearly a week into a fresh fill

[bart6453]

Tested last night and it had dipped to ~50ppm. Added Baking Soda per Pool Calculator. Hopefully everything evens out. SO far so good nearly a week into a fresh fill

I think a good place to start is with Nitro's approach to water maintenance.

As far as I understand you will need to add borates if you already have not to help stabilize the ph.

Again, take a look at nitro's thread on water maintenance on this board. It is a great place to start with water maintenance.

[NewB@Spa]

I am definately a Nitro devotee. Although the last two days I am a bit concerned, I had to add ~5ppm after a soak (1 person about 1/2 hour) is that too much or to be expected? Once I switch over to bleach should I just throw in ~3ppm (per person) after any soak

[chem geek]

I am definately a Nitro devotee. Although the last two days I am a bit concerned, I had to add ~5ppm after a soak (1 person about 1/2 hour) is that too much or to be expected? Once I switch over to bleach should I just throw in ~3ppm (per person) after any soak

Assuming you don't have an ozonator, your soak of 0.5 person-hours would need roughly 2.5 fluid ounces of 6% bleach or 1.5 teaspoons of Dichlor or 3 teaspoons of non-chlorine shock (43% MPS). In 350 gallons, this is an FC of around 3.5 ppm. If your spa is smaller, then the FC level would be higher. You don't add or increase to an FC amount to handle your bather load -- you add a certain physical amount of oxidizer independent of spa size. The FC level is what you want to target after that bather load gets handled and is there to keep the spa sanitary until your next soak.

Now realistically, there is this daily chlorine demand even with no bather load so the rough rule-of-thumb really has two components -- a % daily loss relative to some FC level and an absolute consumption due to bather load, but for simplicity since the bather load is the largest component, we just focus on that, especially since it's the main reason people don't use enough oxidizer -- they have 2 people soaking for an hour and expect that it will take the same chlorine as 1 person for a half-hour, which of course it won't.

[NewB@Spa]

I do have an ozonator, so how does that affect my chlorine treatment, My CD (zero bather load) is about 2.5ppm. My tub is ~425 gallons, but before you have stated that this rule of thumb is irrespective of tub size? So theoretically if 2 people soak for 1/2 hour (=7ppm consumption due to bather load) I should add bather load(7ppm)+Normal CD(2.5) for a total of 9.5?

[chem geek]

It doesn't work that way because your ozonator will presumably oxidize a lot of the bather waste so that the chlorine doesn't have to. So the downside to an ozonator is that when you aren't using the tub every day (i.e. no bather load for a day or more) then the oxonator is oxidizing chlorine itself so your chlorine demand will be higher. However, when you do use the tub, it should oxidize some of the bather load so your chlorine usage would be lower. So you are in better shape with an ozonator if you use the tub frequently and should have a lower chlorine demand (i.e. the rule-of-thumb doesn't apply and your usage may be half or less of that amount), particularly with higher bather loads. If you use it infrequently or with lower bather loads (say, 1 person soaking 20 minutes in a larger 500 gallon tub) then the ozonator may result in your using more chlorine than you would if the ozonator wasn't there.

As for how much chlorine you should use, just add whatever amount is needed so that you have a 1-2 ppm FC residual by the time of your next soak. If you don't soak every day, then you may need to add chlorine anyway in order for it to not get too low -- that sounds like your situation (unfortunately). 2.5 ppm FC chlorine usage with no bather load does sound pretty high, however, so either your ozonator is pretty darn powerful or you've got something else going on in your tub consuming chlorine. If the filters haven't been cleaned recently, then you should probably do so since dirty filters consume more chlorine (because there are more organics trapped in them for chlorine to oxidize -- especially if there's a lot of hair in the filter).