What causes Foaming?

[TreeFiter]

Recently, I've seen a few different situations where foam has developed as the result of a chemical reaction within the pool. I'm curious if any of you have any insight into what is going on, and what this reaction might be telling me about what is in these pools.

The first situation I saw today. I was adding salt to a pool that was just opened. The water was black, this pool was a swamp. When the salt mixed with the water, there was a vigorous bubbling that resulted in a foamy layer on the surface. I suspect this might have been a reaction between ammonia and the salt, and the fizzing was chlorine gas. Does this make sense? If the chlorine is off gassing, does that mean that whatever salt caused the reaction has been consumed, and will need to be added again?

The second situation I see a few times every season. When adding pH increaser, the water returning to the pool becomes very cloudy, and fizzes. As fizzing progresses a foam across the entire surface of the pool. As the water circulates, the layer of foam begins to break apart like little icebergs. The "icebergs" float around and continue to break up, but they maintain sharp corners. They really look like a layer of ice breaking up. I haven't been able to figure out why some pools seem to do this while others don't. I'm wondering if there is something that will react with pH increaser that would cause this. Could this be a reaction with ammonia?

Any thoughts?

 

[Casey]

Black water would have virtually no chlorine or it would not be black. Salt is not consumable and the only way to remove it from the water is with water replacement. Your first theory does not make sense.

Second scenario... maybe high CH levels reacting with pH up?

A complete set of test results on each pool could tell us a lot instead of wading through it blindly like I just did.

 

[chem geek]

Foaming is from soap-like substances which are salts of fatty acids. In general, they are surfactants so tend to bind to each other in thin films on the surface of water. When there is gas, it can push up from the water and create a soap bubble and if there are a lot of small gas bubbles they can form many soap bubbles creating foam. So what is most likely is that the soap film was already on the water and your adding something to the water created or released gas bubbles that then rose and created the foam.

I don't know what would react so much with just adding salt. That's usually pretty innocuous. As for pH Increaser, that's likely sodium carbonate so having gas bubbles in that situation makes sense since the TA and pH are high locally so you can outgas more carbon dioxide in that case. For foam, however, you'd still need the soap film on the water.

 

[TreeFiter]

Could the reaction with the salt be due to HCl? The pH in the pool was pretty low, so I'm wondering if there could be HCl present.

As for the soapy films that cause the foam, what is the best way to get rid of them? Does Chlorine eat them up, or do I need to rely on defoamers and things like that? Where do these soapy films come from? Is it just the oils in our skin and suntan lotion?

The link below is a video of the reaction with the salt. At first it just looks like cloudy water in one area, but later in the video you can see what look like mushroom clouds of gas coming to the surface.

https://www.youtube.com/watch?v=zu9tdK7oeOA&feature=youtu.be

 

[JasonLion]

Chlorine will eat up foam, but it can take a while. Since you will probably be SLAMing the pool anyway, letting the chlorine take care of it is probably the best bet in this case. In pools with clear sparkly foaming water some people use enzyme treatments to cut down on the foaming.

 

[chem geek]

I don't think the pH is low enough to produce enough chlorine gas and you'd likely smell that if that was what was happening. Maybe it's just displacement of leaves and material at the bottom that have bubbles of gas below them. If you were to use a pool sweeper brush and get a similar effect then that is the explanation. I know that there are products such as ProTeam® System Support (see the video linked on that page) that generate carbon dioxide to raise debris. The product uses sodium carbonate peroxyhydrate (aka sodium percarbonate) that in water produces sodium carbonate (pH Up) and hydrogen peroxide..

 

[SwimAustin]

Salt can provide a nucleating site for dissolved gases. Cold water dissolves gases than warm water, so a warming pool might be saturated (or super saturated), then adding anything with sharp edges like salt could cause bubbles. This is the Mentos in Diet Coke affect. There is no chemical reaction happening. Salt is very inert. I can't think of anything in a pool that could chemically react with salt and produce a gas.

 

[TreeFiter]

The pH was fairly low, but not excessive. Maybe 6.8 or so. I did not smell chlorine gas. I don't know about displacement of leaves and debris. The amount of salt was fairly small. I was pouring the bags of salt into the skimmer and a small amount spilled into the pool. Maybe a few cups.

The water was fairly warm. The super saturation idea kind of makes sense.

It was certainly strange, whatever was going on. First time I've seen it happen in over ten years.