SWG and automatic pool cover?

[padrino]

Having an automatic pool cover on the pool in my new house replaced, it was paid for by the seller as part of closing since the old one doesn't work any longer. In any case the installers came out today to install the cover, due to ordering the improper cover they will be back but after my wife mentioned I was installing a SWG they said do not because the salt will corrode the guide rails and mechanical components of the cover. I know salt can be corrosive but I didn't think I would have a big issue at 3000-3200ppm, anyone have insight? I really enjoy the low maintenance of the SWG and don't want to give it up at this house unless I work a good alternative.

What alternatives make sense, does the fact that this pool is gunite have any bearing on the use of an SWG. vs. liquid chlorine (I know in the end the same thing comes up, just gradually with the SWG), vs. other sanitizer options?

 

[Bama Rambler]

Depending on what metals the rails etc are made of, the salt may indeed attack the metal. Or the installers/sellers may just be playing a little CYA (not the stabilizing kind)

Alternatives that make sense are a liquidator or a peristaltic pump to add liquid chlorine to the pool automatically.

 

[padrino]

Depending on what metals the rails etc are made of, the salt may indeed attack the metal. Or the installers/sellers may just be playing a little CYA (not the stabilizing kind)

Alternatives that make sense are a liquidator or a peristaltic pump to add liquid chlorine to the pool automatically.

Thanks for the pointer... I just started reading about the liquidator, I like the idea of something like that.. Sounds like a safe approach that will cover me if there is an issue with the cover and they deny a warranty claim because of the SWG.

 

[Poolsean]

Which brand of automatic cover is it? Some contractors will put a sacrificial anode to protect it. But by all means, make sure they bond it properly.
Adding Sodium Hypochlorite will also be adding salt to your pool. Did they happend to caution you on not using bleach?

 

[padrino]

I'm not sure what brand it is, the cover was paid for as part of closing for my new house, looking for the invoice now.

They only cautioned about Salt, no mention about using other options or what is available if I already have Salt. I need to find the manufacturer and go from there...

 

[chem geek]

The railings/tracks and header tube for the automatic cover are likely to be aluminum. Are the railings underneath coping that overhangs the pool? Or are they on top of the coping (i.e. does the cover ride on the water at nearly that level even at the railings or is it on top of some of the coping as well)? Also, is the header tube above the water level or is this a "vanishing cover" where the header tube is immersed in the water?

My pool builder has installed many SWG systems with automatic pool safety covers and he said the only issues he had with the higher salt levels in SWG pools is for vanishing covers with the immersed header bar. A sacrificial anode buried in moist soil and connected to the bonding wire (which is connected to the header bar and railings of the cover) was needed to prevent corrosion. However, his installations were new where the railing for the cover were under the coping.

If the aluminum track is on top of the coping, then you can get corrosion such as seen in this post where salt splash-out builds up with evaporation. This also happens in non-SWG pools, though not as quickly as the salt level is usually lower if there is reasonable water dilution from backwashing and rain overflow (for outdoor pools). At 2 ppm FC per day using chlorinating liquid or bleach, this adds around 100 ppm salt per month so 600 ppm in a 6-month season. Plaster pools normally start out with around 300 ppm salt (525 ppm TDS, the rest being mostly calcium and bicarbonate). If the pool is diluted by 1/3rd each season, then the salt level will bounce between 1200 and 1800 ppm each year.

Using CYA in the water cuts down the corrosion rate for any metal that is immersed in the water. There were reports (on another forum) of stainless steel corrosion in an indoor SWG pool with 3-5 ppm FC and no CYA but that's a rather high active chlorine level. When CYA is used and the FC is around 10% of the CYA level, then the active chlorine level is roughly the same as a pool with only 0.1 ppm FC and no CYA.

 

[padrino]

Thanks for the information, there are some great details here...

I found that the pool cover is from Pool Cover Specialists, the rails are aluminum and they are underneath the coping. The pool was built with an older version of the same cover so the mechanism and everything is recessed in the end of the pool below water level but nothing sits in the water at all times.

The company that was doing the install showed up yesterday and finished it when no one was home so I didn't get a chance to talk to anyone but I will follow-up and ask about the possibility of a sacrificial anode.

In the end do you think it's just too much trouble since I haven't installed a SWG in this pool yet?

 

[chem geek]

You don't have to do anything until you get an SWG and even then the risk is low since the rails are not on top and the aluminum header sounds like it stays above the water -- this is like my pool cover. A sacrificial anode on the bonding wire will reduce the risk of metal corrosion for ALL metal that could possibly be in contact with the water. If they connected the aluminum rails and header tube to the bonding wire as well, then everything would be protected. Not essential, but an extra safety factor if you wanted it.

 

[padrino]

Thanks for all of your help.. The company is based a few hours away so it looks like having this taken care of by them will be a bit of a challenge. I wanted to catch them before they came back but no luck.

I picked an IC40 for this pool, assuming I'm going to do what you suggest myself would you mind pointing me to the proper material to use for the anode along with the basics of how to connect? I'll give it a shot.

 

[bk406]

assuming I'm going to do what you suggest myself would you mind pointing me to the proper material to use for the anode along with the basics of how to connect? I'll give it a shot.

Most of the time you would use zinc. Howerver, since you are trying to keep the aluminum in your cover from becoming corroded, you want to use magnesium. If you used zinc, the aluminum would act as an anode to the zinc and corrode before the zinc would.

Google up magnesium anode and you should find something. Just connect it to the bonding wire and bury it in a flower bed. You should be able to get to the bonding wire near the pump or close to any other equipment.