Sacrificial Zinc Anodes for Saltwater Generators

[Tadpole]

Is this a "must" have item, a "should" have item or a "waste of money" item for salt water pools?

If this is something that I should have, which type should I go with? The disk that you throw in the skimmer basket, the one that bolts to your ladder or the one that's installed in the plumbing?

Thanks, Joe

[PoolDoc]

Funny you should ask. I need to buy some to try them.

There doesn't seem to be any reliable information about how well they work on pools with salt. I can tell you (for almost certain) that tossing an anode in a plastic skimmer basket is useless. Putting one on the latter would tend to protect the ladder might, or might not protect anything else, depending on the bonding -- if you have a heavily corroded aluminum ladder anchor, or worse, a plastic anchor, you will ONLY protect the ladder.

Putting a zinc anode into the plumbing is probably useless, unless you are able to tie the anode to the pool bonding system.

The problem is that anodic protection is an ELECTRICAL process, and unless you establish the right electrical pathways, all the zinc in the world won't help a bit. Sound complicated? Apparently, it is. What I can tell you is, it's a complex subject without clear answers or established solutions.

I pestered these guys for a couple of days:
http://www.rotometals.com
and they ducked. They do big ship anodes designed and spec'd by corrosion engineers and are risk-averse. So they won't recommend ANYTHING. I'm probably going to buy these
http://www.rotometals.com/product-p/zincplate5x6x12.htm
and from them, for my own use. My personal concern is the $11,000 15HP cast iron and bronze pump I just rebuilt. This pump is on a 200,000 pool I'm converting to salt.

So, I'm going to be doing some experimenting. We'll see how it goes!

Ben

[Poolsean]

Ben and Joe,
Sacrificial anodes are more of an early warning or protection device. They will erode before your harder metals (ladders, handrails, heat exchangers) do. The one that looks to be the best available, is from Pool Tool. Slip x Slip Inline Anode #104-D, www.pooltool.com. This fits Ben's description of the anode with a connection to a pool bonding system.

In my opinion, a Sacrificial Anode is not needed for a pool that is properly bonded and working properly. For older pools or questionable pool bonds, the sacrificial anode is a good idea, but it is not the ultimate solution. Once its been determine that there is a poor bond, it must be found and repaired.

[PoolDoc]

Sean,

I understand the position, and I hope you are right. But I'm still going to put the anodes on the Marlow pump I have.

BTW, when there's more time, I'll be interested in your reactions to what I'm doing and experiencing. Currently, I've got a 200,000 gallon pool on salt with HEAVY (>400 ppl/day) loads that are being carried by two IC60's and about 25# of cal hypo over 10 days. Levels are holding at 10 - 15 ppm FC with ~120 ppm CYA. (I'm going to take the 4 points off on the inspection. I don't expect much grief; the inspector asked my last year if I would consult with some of the motel pools in the area that were using salt with disastrous results.) Any how, I'll be adding two more IC60's by weeks end, and have the capability to add 1 more beyond that. But with 2 units holding at 80% duty cycle, I think 4 units at 60% are likely to be more than enough.

PS. pH has been DROPPING!

[chem geek]

There are some materials that are more susceptible to corrosion at higher salt levels. Though obviously low-grade stainless steel and naked steel and zinc are problematic, they aren't usually used in pools in the first place (high-grade stainless steel is used instead). However, aluminum is used in automatic covers and if the header/leader bar is immersed in the water as it is for "vanishing" covers, then it can corrode more quickly. My PB ran into this problem on all pools he installed with such vanishing covers where they were OK in non-salt pools but corroded rather quickly in salt pools. The cover manufacturer recommended using a zinc anode which he did and has not had any problems since.

The key, as Ben mentioned, is to electrically connect the anode to the metal you want to protect and since that metal should be connected to the bonding wire, you can just protect everything on the bonding wire by attaching the zinc anode to it. The zinc anode is ideally then buried in moist soil (i.e. to "ground"). The net effect of all this is for the oxidation of the zinc to put electrons onto the wire essentially putting a small negative voltage on everything connected to the bonding wire. This essentially raises the overvoltage that needs to be overcome for the protected metal to corrode -- any metal trying to give up its electrons has more work to do so since there is already a negative voltage (extra electrons) trying to stay with the metal atoms.

[Tadpole]

I appreciate all the info, guys. Most of it is too technical for me. I'll just save my money on the zinc and use it to replace my ladder and such a few years down the road.

Thanks again!

[Poolsean]

Ben,

Using the following parameters for your pool, 200,000 gallons, circulation pump running 24/7, outdoor location, flat water (no water features), peak water temp of 86 degrees, and a maximum bather load of 500 ppl throughout the day, you need around 10 lbs/day of output to maintain residuals of 2-3 ppm.
The two units holding at 80% duty cycle, is this with the addition of the 25# cal hypo too? You will probably need to add the other two, and you mentioned having space for one more, which I would predict you will need, THEN you can greatly reduce the amount of cal hypo you are supplimenting with. (5) IC60 cells running around 40 -60% would be what I think you'll end up with.

As to why the pH is dropping... what is the pH of your source water? I'm sure you've experienced the steady to increasing pH of salt systems, so for it to be dropping, there's usually an outside interference causing this.