Help with appropriate shock for vinyl in-ground

[jeepers]

Hi -

I tried searching the forums but couldn't find an appropriate answer to my question. I have a vinyl in-ground pool and am getting conflicting information about what type of chlorine shock to use.

I was concerned about handling/storing liquid chlorine and found the Lithium Hypochlorite to be very expensive, so at the advice of my local pool store I have been using bags of Calcium Hypochlorite. I am very concerned about bleaching and/or weakening of the liner, so I have diligently tried to dissolve the powder in a bucket before adding to the pool, but always have a residue collect in the corners of my deep end hopper. I just read elsewhere today that I should pre-dissolve and then just pour the liquid into the return stream, disposing of any remaining solids. (My pool store never mentioned about the disposal of the solids).

Can you confirm that Calcium Hypochlorite is appropriate and safe for vinyl liners if pre-dissolved? What is the residue and I can I just throw it away? Are there any other products that I should be considering? Incidentally, I concurrently use a floater with 3" tabs.

Thanks.

Jim

[Watermom]

Hi, Jim, and welcome to the Pool Forum!

Cal-hypo is ok to use, but vinyl pool do not need calcium. (The residue will eventually dissolve.) Another choice (and what most of us do) is to just use plain, household bleach for your source of chlorine. Works great, inexpensive no residue left behind, readily available. Many of us use Walmart's generic 6% bleach. It is sodium hypochlorite just like liquid pool store chlorine is but just a different concentration. (Pool stores typically sell either 10 or 12.5% sodium hypochlorite.)

The trichlor tabs in a floater are fine for awhile but they are stabilized meaning they add CYA. All pools need some CYA but when you get too much, you have problems.

Test a set of current water testing results taken with a drops-based kit. Also, tell us the volume of the pool and the type of filter you have.

You'll need a good test kit if you don't already have one. The one we recommend is the Taylor K-2006 or 2006C (same kit, larger bottle of some reagents). If you buy it through the Amazon link in my signature, the Pool Forum makes a little money on the sale which helps us keep this form online. Only buy if the seller is Amato Industries, however. Some other sellers are substituting the K-2005 which you do NOT want.

Hope this helps!

[SalemCastles]

If I might ... it depends on number of factors that need to be considered. Firstly, I ran 37 ppm CL using Cal Hypo broadcast directly around the pool when I opened this year with no bleaching of my liner (not saying anyone else should). The instructions on the HTH product say to broadcast it directly in the deep end. I too get some residue on the bottom that the robot picks up but now tend to dissolve it in a bucket first to avoid that. The other factor is how much Calcium is in your water to begin with and what your annual water replacement is. This is true also of CYA. Being in Ontario I have to close my pool for the winter and can count on at least half of the water being replaced every year. So I can run the season without getting to levels that cause problems. Bleach is not the best value for me in my market area or I WOULD use it ... I'm just suggesting that it's not the only option based on the other factors.

[jeepers]

Many of us use Walmart's generic 6% bleach. It is sodium hypochlorite just like liquid pool store chlorine is but just a different concentration. (Pool stores typically sell either 10 or 12.5% sodium hypochlorite.)

Thanks for the friendly welcome. This is a really great site.

I have done some reading on the BBB method and am intrigued. I'll post my most recent numbers when I get home from work, but as of last check I've got my pool seemingly dialed in with current (albeit expensive) regimen. I'd certainly be interested in converting to a more cost-effective system, but don't want to mess anything up.

Can I transition into a modified BBB? I expect that the calcium hypochlorite will be the first thing that I'll run out of. If so, how much 6% bleach would I use to shock a 25,000 vinyl pool? Can I continue to shock with bleach but use my 3" pucks in the floater?

Thanks.

Jim

[aylad]

In a 25K gallon pool, each 2 gallons of 6% bleach will raise your FC by 5 ppm, so you can use that as a guide. As to how high your chlorine needs to go, that will depend on your CYA level. If you can see the blue links at the bottom of Watermom's sig, click on the "best guess chlorine" table to tell you how high your Cl needs to go, based on your CYA level. You can absolutely shock with bleach and still use your tabs in the floater, IF your CYA level is not too high--most folks keep it around the 40 ppm range.

Janet

[jeepers]

In a 25K gallon pool, each 2 gallons of 6% bleach will raise your FC by 5 ppm, so you can use that as a guide. As to how high your chlorine needs to go, that will depend on your CYA level. If you can see the blue links at the bottom of Watermom's sig, click on the "best guess chlorine" table to tell you how high your Cl needs to go, based on your CYA level. You can absolutely shock with bleach and still use your tabs in the floater, IF your CYA level is not too high--most folks keep it around the 40 ppm range.

Janet

Thanks, Janet.

Here are my numbers from 6/24:

FC 1.5
TC 1.5
CC 0
pH 7.7
Hardness 230
Alk 83
CYA 25
Copper 0.1
Iron 0

I brought the ALK up slightly after this test. I use 3" tabs in a floater and shock every 7-10 days with Calcium Hypochlorite.

I'll review the Best Guess chart again this evening. I looked at it briefly at work today but wasn't quite clear on how to read it so I'll see if it makes more sense now.

Jim

[aylad]

Why do you shock it so often? Unless you're having a problem, see algae starting, or are losing chlorine overnight, there's really no reason to shock it on a regular basis. However, with your CYA at 25, you need to keep the chlorine between 3 and 6 ppm at all times. Be careful about shocking with the cal-hypo, though--your calcium level is climbing, and it won't be too much longer before you start having cloudy water issues due to the calcium....

With the best guess chart, the left-most column shows your CYA level, the next one shows the minimum and maximum chlorine levels that you need to keep in your pool for that CYA level, and the next column shows how high you need to take your chlorine to achieve "shock" level. The right-most column is for those who have mustard or black algae, or some other water problem that does not respond to normal shock levels.


Janet

[jeepers]

Why do you shock it so often? Unless you're having a problem, see algae starting, or are losing chlorine overnight, there's really no reason to shock it on a regular basis. However, with your CYA at 25, you need to keep the chlorine between 3 and 6 ppm at all times. Be careful about shocking with the cal-hypo, though--your calcium level is climbing, and it won't be too much longer before you start having cloudy water issues due to the calcium....

With the best guess chart, the left-most column shows your CYA level, the next one shows the minimum and maximum chlorine levels that you need to keep in your pool for that CYA level, and the next column shows how high you need to take your chlorine to achieve "shock" level. The right-most column is for those who have mustard or black algae, or some other water problem that does not respond to normal shock levels.


Janet

Thanks again, Janet -

So to confirm that I'm understanding the Best Guess chart, assuming that my FC is 1.5 and if I round my CYA up to 30, would I add approximately 5 gallons of 6% bleach to achieve an acceptable "shock" of 15 ppm?

For my current practice, my local store recommended shocking 1x/week with the Calcium Hypochlorite. I've extended it to once every 10 days or so but now realize that even this may be overkill. The kids are in it literally every day so I've been trying to avoid getting behind the 8-ball with the chemicals.

Another question: the pool store told me to keep the FC between 1-3ppm. They didn't seem concerned about the CYA so long as my FC level stayed within reasonable limits. Should I be keeping it higher?

Jim

[PoolDoc]

The Best Guess page -- linked in my signature -- answers most of the questions you asked. Read it, and then we'll try to answer those that remain.

[Watermom]

Also, trichlor pucks are stabilized which means they add CYA. So, if you are going to continue to use them, you'll need to check your CYA every week or two. For every 10ppm of chlorine that the pucks add, they also add 6ppm of CYA. When your CYA hits about 50, you'll need to stop using them or your CYA level will get too high. At that point, just use bleach for your daily chlorination needs as well as shocking when necessary. (I rarely shock my pool. As long as you don't let your cl level fall lower than the minimum on the range listed in the Best Guess chart, you shouldn't need to shock.)