White crusty build-up in Stenner injector for 5-10% bleach

[kabbak]

I have to drill (5/32") out the black plastic injector every 10 days or so due to plugging with the same sort of white deposit that plagued my prior liquidator setup.

The removed deposit dissolves in water acidified with Muriatic acid.

Diluting the bleach with water into the Stenner from 10 to 5% didn't seem to help. Bleach is 10%, HDX brand from Home Depot. OSH equivalent has same effect. Both claim "Calcium free."

The injector is at the top of straight section of 2" PVC return pipe to pool.

Stenner peristaltic pump is model: 45M1, 3 gallon / day set at 7.

Since the bleach in the Stenner black plastic tubing only gets this deposit near and at the injector, there must be some reaction with the pool water that forms the local deposits.

My recollection is the problem worsens with increased temperatures. Perhaps because solubility of some salts DECREASES with increasing temperature? Or the pump is running longer. Problem occurs in 50F water and up. I also believe this problem began many months after installing the Stenner pump in 2018.

Of course, I use the BBB method. CYA: ~40, TA: 80, CH: 320, pH 7.7 (tap water is over 8.3).

Anybody have any insights into taming this beast?

Thanks much!

 

[JoyfulNoise]

The pH of bleach is anywhere from 12.5-13 and so right at the injection point you will locally have very high pH. This can cause calcium to scale on the tip. Also, if you’re not in the habit of flushing out the Stenner tank regularly with clean water, the bleach that sits in there will build up more salt in it over time. The higher the salinity of the bleach, the more lonely it is to cause scaling.

Does the injector tip have a check valve on it? If the injector is bad, it could dribble out small amounts of bleach over time that would lead to scaling.

 

[kabbak]

Marvelous reply. Thank you!

By "salt" do you mean Sodium Chloride or other salts like, Calcium? I assume Sodium from the Sodium Hypochlorite decomposition into the air?

I will purge the tank and monitor things.

I have no check valve in the tank > stenner pump > injector to pool return plumbing. If the Stenner peristaltic mechanism leaks from the siphon pressure head (+-6" max) that might be an issue. I could test it. When tank is low reverse siphon leakage would pull pool water into Stenner feed and its high pH.

Are other's not experiencing this problem?

Is a sodium test strip likely to work in the bleach tank to give me relative salt readings?
How might I measure pH in the bleach tank. Would high pH test strips be necessary?

Thanks again!

 

[JoyfulNoise]

All bleach and liquid chlorine is a mixture sodium hypochlorite, sodium chloride, sodium hydroxide (lye) and water. The sodium chloride and lye come from the manufacturing process, there is no way to get rid of it and the lye is needed to raise the pH of the end product so that the sodium hypochlorite remains stable during its shelf life.

You can not measure the pH or chloride content of bleach directly as the hypochlorite would interfere with those measurements.

I’m not an expert in Stenner pump installations but I believe that it is recommended to have a check valve inline with the injection port to ensure that water can only flow one way and that there is no siphoning into or out of the tank. I would wait for a reply from someone with a Stenner pump to chime in.

 

[tim5055]

I believe that it is recommended to have a check valve inline with the injection port to ensure that water can only flow one way and that there is no siphoning into or out of the tank.

Correct, a check valve is advisable. It is not uncommon for the the tubing under the rollers to develop a crack which is why they should be replaced at least once a year. A cracked tube and no check valve can cause a mess. I alwasy kept a few spare tubes on hand.

If I remember, what Stenner calls a high pressure pump comes with a check valve, the low pressure pumps you buy it separate.

 

[kabbak]

Gentlemen, thanks very much for the detailed description of bleach chemistry (very helpful) and the Stenner observations and recommendations.

FWIW, my Stenner is several feet above the chlorine tank liquid level and pool return pipes so I gambled I'd be ok without the check valve. However, I will now rethink this based on the chemistry and leakage issues discussed.
If I come to a solution (pun may be intended) I will post it.
You guys rock.

 

[Stenner Tech Support]

Good morning!
If your system is 25 psi or less a check valve is unnecessary. The pump head itself acts as the check valve. We do recommend using our injection check valve if the system is 26-100 psi. If you ever notice back flow into the solution tank (while using our Classic Series models) it is more than likely due to a worn tube, or your roller assembly not being fully expanded. We have literature completely free and accessible on our website that gives step by step instruction on tube changes and roller expansion.

 

[yottabit]

Did you ever find a solution to the crystalline buildup? I'm encountering the exact same issue, using 1/4" tube without the check valve. Did you add a check valve? Did it help at all?