Using Zinc anodes in a pool?

[drwpweb]

Hi everyone I have a quick question for you…Can you use sacrificial zinc anodes in a surge tank to help prevent corrosion without affecting the chemistry of the pool? We have valves in our surge tanks that are cast iron. They are old, however we are trying to prolong the life of them and have recently came up with this idea. There is little on the web about using them in a pool environment, and I know you can actually sanitize the water through zinc, however I just don’t want it messing everything else up.

We use cal hypo as the sanitizer, cyanuric acid as stabilizer, and hydrochloric acid to balance.

 

[JasonLion]

Sacrificial zinc anodes are sometimes used with aluminum frame automatic pool covers to reduce the rate of aluminum corrosion.

Zinc isn't used much with pools. I presume that at high enough levels in the water you can get zinc staining, just as you can with copper or silver, but I don't know for sure.

 

[chem geek]

Instead of placing the zinc anode inside, just connect it electrically to the tank and put the zinc anode into good contact with the ground (i.e. properly ground it). The zinc will start to corrode and place a small negative charge on the wire and tank and that will help prevent corrosion of the tank. The idea isn't to create a complete electrolytic cell with complete electrical and ionic paths, but rather just to set the electrical potential of the tank more negative to lower its likelihood of corrosion. It's not as effective as a full electric/ion path, but it is better than nothing.

The "zinc" sacrificial anodes used to protect the aluminum leader in pool covers are put in a open-bottomed box in the ground and just replaced every few years when they are mostly corroded. The zinc itself never gets into the water. I was surprised this works because there isn't an ion path, but it turns out to be enough to prevent corrosion from being as rapid and when I looked into it more I saw that it was similar to connecting a battery with the negative end to the tank and the positive end to a ground source where the positive end in the ground would tend to corrode. The key is connecting to "ground" that acts as a seemingly endless source and sink of electrons, at least enough to produce a small potential difference. Though a charge buildup prevents current flow, that's OK because a negative charge on the tank reduces its likelihood of corroding.

Technically, aluminum needs to be protected with a magnesium block, not a zinc block, since zinc has a higher reduction potential than aluminum. I'll have to ask my pool builder about that -- I suspect they just call these the same thing when they're not. [EDIT] The reduction potential isn't the same as the order in the galvanic series due to over-potential (activation energy) so zinc still protects aluminum. [END-EDIT] The pool cover people were the ones who actually did the sacrificial anode protection and the pool builder was just told about it and didn't do it himself.

Richard

 

[Aquaman95]

Yes you can. Most steel body commercial filters have sacrificial anodes in them for the same reason. I'm not sure if they're zinc or magnesium.

Is your surge tank metal like a filter tank or is it built on site out of concrete?

You can get the anodes from a yacht dealer or most commercial filter manufacturers like Miami Tank or Eureka.

 

[duraleigh]

I do not know what a surge tank is or it's purpose in a pool.

 

[Aquaman95]

I do not know what a surge tank is or it's purpose in a pool.

Surge tanks or pits are most commonly used in commercial competition pools that have gutters instead of skimmers.

Basically they are designed to not lose water to splashout during heavy bather loads, to provide a smoother water surface for competitive swimming, and to reduce suction entrapment concerns.

You may have noticed in a skimmer pool that has a lot of people in it some water can splash out on the deck and then when the swimmers exit the pool water level is lower. This is because each body displaces some water...with enough bodies you lose water.

In a gutter pool the water displaced by swimmers overflows in the gutters and is collected in a tank or pit on the suction side of the pump that operates on a system of floats much like a toilet tank. When the swimmers exit the pool the water is returned through the returns. pits also operate on the theory that "water seeks it's own level". Gutter pools are also faster swimming pools because there is no "slap back" effect from the pool walls like in a skimmer pool that can make the water choppy and thus slower for competitive swimmers. Additionally, since there is no direct suction on the drains because the tank or pit is prior to the pump, suction entrapment concerns are alleviated.

 

[duraleigh]

Thanks.....good explanation.

 

[drwpweb]

First of all, thanks everyone! So would the anodes get attached to the concrete wall, or so they need to be touching the metal they are protecting? All our surge tanks are built out of concrete.

I attached some pictures from our last expansion to show those of you who don't know what a surge tank is...They aren't from the exact surge tanks I was refering to, however I don't have any pictures of them on me. But it gets the idea across from those who don't know.

The second picture shows what it looks like under construction, on the upper left you can see part of the pool, and as mentioned below their main use is for balancing. The water level in the tanks is equal to the level in the pool when filled. All of the floor drains drain directly to the tanks, as you can see with all the pipes going in. The pumps will eventually sit on the green pipes and all of the tall pipes as well as the holes on top of the tank all go out to some part of the pool.

The first picture is that same tank done with the motors and pumps installed, all of the pipe that goes back into the tank actually goes out to soome part of the pool. (In this case, this is a river ride, so it goes to effects over the river, propulsion for the river, and to the filters)

 

[JasonLion]

The anodes need to be electrically connected to the metal they are protecting. Typically you connect them to the bonding grid, since that should already be connected to everything metal that touches, or gets close to, the water.