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Adding Chlorine Bleach Very Slowly--why/how/what?


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chem geek said: "When adding chlorine (bleach or chlorinating liquid) do so VERY slowly over a return and to be extra safe, you can predilute it in a bucket of pool water (say, 2 cups of chlorine in a 2+ gallon bucket, then add that slowly, repeat). This is just being extra cautious -- for Cal-Hypo you would always pre-dilute, but for chlorine pouring very, very slowly is usually OK, but most people become impatient so using pre-dilution kind of forces one to slow things down."

I couldn't find this by searching:

Can you explain more about adding bleach very slowly and also about pre-dilution? Does it change the effect on pH? I would appreciate a good, long, geeky explanation.

Tom Haws

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When you add a concentrated chemical to water, it gets diluted as the chemical mixes with the water. If you didn't have circulation, the natural process of diffusion would be very slow. This link has some movies showing the speed of dye in gel and in water (these are lower on the page, not quite half way down). If you click on the one on the right, you'll see that after the initial physical movement of the dye, the mixing slows down a lot.

You can readily calculate the effect by figuring out the pH and FC adding a quantity of bleach to different amounts of spa water. Let's say you add 3 fluid ounces of 6% bleach to spa water that starts out with a pH of 7.5, TA of 60 ppm, CYA of 30 ppm. The resulting pH and FC will be the following in various volumes of water:

1 cup: pH 10.3, TA 10,265 ppm, FC 23,146 ppm, Active Chlorine 17.5 ppm

1 gallon: pH 9.48, TA 1087 ppm, FC 1447 ppm, Saturation Index +1.48, Active Chlorine 9.7 ppm

10 gallons: pH 9.06, TA 103 ppm, FC 145 ppm, Saturation Index +1.34, Active Chlorine 2.4 ppm

50 gallons: pH 8.72, TA 81 ppm, FC 29 ppm, Saturation Index +1.09, Active Chlorine 0.55 ppm

150 gallons: pH 8.25, TA 67 ppm, FC 9.6 ppm, Saturation Index +0.67, Active Chlorine 0.15 ppm

350 gallons: pH 7.81, TA 63 ppm, FC 4.1 ppm, Saturation Index +0.24, Active Chlorine 0.055 ppm

If you add the bleach slowly with water circulating, then it gets mostly mixed with the full body of water fairly quickly -- mostly in under a minute.

Richard

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Richard,

That's very good information. What I still don't understand is the adverse effect of having those very high concentrations until the chlorine is diffused. Do super high concentrations tend to turn to gas or something? What's the main reason you want to mix fast and pour slowly? Is quick diffusion critical? Why?

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Higher concentration of active chlorine (hypochlorous acid) is more corrosive -- it's a strong oxidizer. The higher pH level is less clear since certain materials have no problem with it while others are more of a problem. My best guess is that the high pH might be worse for fibrous materials such as found in cartridge filters, but are probably not as serious for metals or plastics. Think Drano and how it's OK with pipes but breaks down organic materials.

In reality, the exposure is brief so as I said before, some people do add chlorine to their skimmer in pools. I just like to play it extra safe. I see no problem adding something innocuous such as baking soda or even slow-dissolving Cyanuric Acid into the skimmer (the latter gets caught in the filter which then slowly dissolves the CYA with the pump running 24/7), but acids and bases and oxidizers are just a lot harsher.

In practice, the really bad thing for metal is acid and Muriatic Acid is so strong that it remains at very low pH in spite of slowly adding it to a skimmer. It's an absolute no-no. It's pH is -1 so even a 10:1 dilution is a pH of 0 and a 100:1 dilution is a pH of 1.

So I'm probably being too conservative, but at least you have the info. For sure, don't ever add acid to the skimmer. As for the other chemicals, they are less risky.

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Ahh. I am starting to grasp, I think. So it was probably really bad for me to pour a pint of Muriatic HCl right near the edge of the pool without vigorous stirring. As for the bleach, perhaps it is not so critical. Am I getting it?

Tom

Tom,

Yup. If you pour acid near the edge of a pool, then that edge can deteriorate, either plaster or vinyl. You should instead pour strong acid only very slowly over a return flow with the pump running, especially in the deep end if you have a floor drain. That will ensure the best mixing. For extra safety, you can lightly brush the side and bottom of the pool where you've added the concentrated chemical. Most reports of people having vinyl pools fail is when they dump a concentrated chemical such as Cal-Hypo, bleach or acid quickly in one place where it then settles to the bottom because it is denser than water and didn't get mixed. So it sits at the bottom weakening the vinyl surface.

Richard

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  • 1 month later...

We never thought about adding stuff right way or wrong way - just tried to use common sense.

Acid instructions say only add up to two cups every few hours - pouring it into a skimmer makes no sense - pouring it into output fliter stream is common sense to better disperse this caustic chemical.

I don't worry nearly as much about liquid cholrine except to, of course, have the filter system running long enough to have full max. motion of the water. We have never caused any liner damage pouring in chlorine to shock the system.

Soda ash or soda bicarb have never been thought of as problem causing - unless the wind is blowing hard we can easily disperse these powders by using a large cup and a throwing motion to spread them over a large area with, of course, filter running long enough to create maximum water movement.

Pool chemicals are dangerous - specially acid and chlorine - always take care and use common sense - like always wearing rubber gloves when adding chlorine tabs to your chlorinator.

Good Luck and Good Swimming!

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  • 2 weeks later...

I have been a bleach guy for several years after discovering the problems with cyanuric acid. The problem I was having using liquid chlorine (bleach) was that when I added the bleach the chlorine level would go fairly high, then drop steadily over several days (often to near zero in mid/late summer) until I added more bleach. I had decided to purchase a SWG to ensure a relatively constant chlorine level, but then I came across a product called the Liquidator (I believe it was on this forum) that would allow liquid chlorine to be added to the pool in consistent amounts while the pump runs. Since this product was only ~$140, I thought I would give it a try first.

The Liquidator is a tank that holds about 20 gallons of water (approximately) and 4 gallons of liquid chlorine. You add the chlorine to the tank through a funnel that feeds the chlorine to the bottom of the tank (chlorine is heavier then water). This super chlorinates the water in the tank. The tank has a water input and output that are connected to the main water lines before and after the filter. The input maintains a constant water level in the tank and the output allows this super chlorinated water to be siphoned into to your pool; the amount is controlled by a valve. It is actually a rather ingenious simple setup and I have been very happy with the results.

So, I add bleach to the Liquidator weekly (2x weekly in mid summer). The Liquidator then adds chlorine to the pool whenever the pump is running (similar fashion to a SWG that creates chlorine while the pump is running). This product has allowed me to maintain a relatively constant amount of chlorine in our pool (my goal).

Anyway, just thought I would share my experience with the community. If anyone is interested I will be happy to post pictures (once I figure out how) and information on where this can be ordered.

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The Liquidator has had mixed results. You can read mostly positive reviews here and some negative reviews here and here. The main problem is that in some pools there is a lot of buildup of "white stuff" which is probably calcium carbonate scale at the outlet valve area of The Liquidator. It appears that for some people, the use of 50 ppm Borates in the pool helps this situation and keeping the saturation index slightly negative also helps a bit.

I initially had higher hopes for this unit until the white stuff problems showed up. Nevertheless, it's inexpensive enough and works well for at least half to two-thirds of people that it's worth looking into.

Richard

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Richard,

Thank you for the feedback.

As I said, my unit is only 1 year old. I noticed in the posts you referenced that may of the problems occurred during the 2nd year. I may be in for problems this year...

While I also have had a buildup of the "white stuff", when I started up my pool a few weeks ago, I thought that this might be calcium build up from hard water, so I put the valves in a mild solution of CLR cleaner and then brushed them with a nylon brush. So far, so good. I will keep an eye on the flow. Oddly, the flow meter is completely clear. The acrylic must resist this build up better then the material that the valves and tubing are made from.

Perhaps a SWG will be in my future.

Mario

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