Use spa jets to aerate water

[SunnyOptimism]

I'm still trying to come up with additional aeration methods. Here's what I have in my pool -

1. Spa spillway

About 2/3 of my return water flows into the attached spa and then spills over into the pool with about a 2 ft drop 18" wide spillway. Lots of air bubbles



2. Natural stone Waterfall

I have a separate pump which pulls water from the pool and sends it gurgling down a waterfall made of stones, boulders and cement. The pump actually splits the water with a three way valve so that about 2/3 goes to the waterfall and 1/3 to and eyeball return. This also produces good water circulation and lots if bubbles at the waterfall



3. Spa water aeration

One other method I can think of would be to run the spa jets on the water in the spa (no heater on) and let that put lots of air into the water and then switch over to pool mode a dump all that freshly aerated water (~1000 gal) into the pool.

4. [PROPOSED] Pool cooler / shower

On my bucket list of to do's is to take some ideas I've seen here on TFP and build a PVC shower/fountain using the eyeball return from the waterfall pump. I'll have to experiment with showers versus fountains but it should be a fun project.

Are there any hard numbers using pool math on how much you can drop the TA using acid/aeration? Or is it pretty much pool specific?



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[chem geek]

It's pool specific since aeration is not an easily quantifiable quantity. You can look at this chart to see how over-carbonated water is compared to air at various TA and pH levels. This is why one lowers the pH for the process and why the lowering of TA is easier at higher TA and slows down as the TA drops. This TA effect is even greater than the chart shows since the outgassing is apparently proportional to the square of the TA level, not more linear as the chart shows.

 

[SunnyOptimism]

It's pool specific since aeration is not an easily quantifiable quantity. You can look at this chart to see how over-carbonated water is compared to air at various TA and pH levels. This is why one lowers the pH for the process and why the lowering of TA is easier at higher TA and slows down as the TA drops. This TA effect is even greater than the chart shows since the outgassing is apparently proportional to the square of the TA level, not more linear as the chart shows.

Ah, the light bulb is slowly flickering on...

So in our pools, there exists a chemical equilibrium of metal carbonates (probably mostly sodium carbonate), bicarbonate's and carbon dioxide gas. As you push the pH of the pool water lower, you force the equilibrium of those species towards higher CO2 levels and the aeration causes that CO2 to be released thus dropping the overall TA.

Does that sound right?


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[chem geek]

Forget the "metal" part which is usually sodium. That will be an ion in the water and separated from the carbonates. Instead think of the carbonates being in equilibrium between carbonate ion (CO₃^2-), bicarbonate ion (HCO₃^-), carbonic acid (H₂CO₃), and carbon dioxide (CO₂(aq)). It is the latter species, the aqueous carbon dioxide, that outgases and is trying to get into equilibrium with the carbon dioxide in the air.

The next part of your description is correct where a lower pH pushes the carbonate equilibrium more towards carbon dioxide. Aeration just increases the physical rate of transfer, but even without aeration there is outgassing -- it's just slower.

The last part of your description is incorrect in that carbon dioxide outgassing does not change TA. What it does is to raise pH with no change in TA. The pH rises because you are essentially removing carbonic acid from the system or another way to look at it is when carbon dioxide gets removed, more bicarbonate shifts to fill in giving up a hydrogen ion that lowers the pH. The reason the TA doesn't change is that the lowering of TA from removal of carbonates is exactly counteracted by the increase in TA from the rise in hydrogen ion (i.e. the lowering of pH). It is the subsequent adding of a strong acid that then lowers both pH and TA. So the process overall looks like the following:

ACTIVITY .......... pH .... TA ... (The following assumes 6.8 is the lowest measurement on the pH test kit)
===================

Acid .................... - ........ - ... Add enough acid to bring pH down to 7.0

Aeration ............. + ....... 0 ... Aerate until pH rises to 7.2
Acid .................... - ........ - ... Add enough acid to bring pH down from 7.2 to 7.0 (you may continue to aerate while you do this)
------------------------------------
Aeration & Acid .. 0 ....... - ... Continue this combination (cycling of the two above) until TA is at the target you want

then AFTER you have reached your target TA,

Aeration ............. + ....... 0 ... Aerate until the pH rises to your target pH (say, 7.5).

===================
Net of Above ....... 0 ........ -

 

[SunnyOptimism]

Very informative post. Thank you.

So if one assumes that the pool water alkalinity comes from CYA, borates (if present) and carbonates, then the acid-aeration method is only affecting the carbonate portion of the total alkalinity.

Excellent


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[VladSI]

If your returns have really good flow - how about this:

Extend one of the returns with some PVC.
Drill a hole in the extension big enough to allow a 1/4" aquarium air line to slip in.
Insert the aquarium line and pull out of the eyeball extending an inch or two.

The venturi effect will create vacuum in the tubing that pulls a ton of air into the water stream flowing out of the eyeball. The bubbles are microfine leading to greater surface area. I have a very crude version of this that screws into the return when I need to aerate and then is replaced by the standard eyeball when not needed.

I can post some pics if you can't picture it.

 

[SunnyOptimism]

If your returns have really good flow - how about this:

Extend one of the returns with some PVC.
Drill a hole in the extension big enough to allow a 1/4" aquarium air line to slip in.
Insert the aquarium line and pull out of the eyeball extending an inch or two.

The venturi effect will create vacuum in the tubing that pulls a ton of air into the water stream flowing out of the eyeball. The bubbles are microfine leading to greater surface area. I have a very crude version of this that screws into the return when I need to aerate and then is replaced by the standard eyeball when not needed.

I can post some pics if you can't picture it.

I get what you're saying but I would love to see some pictures too!

Right now most of my return flow goes into the spa which fills and spills over into the pool. I can easily adjust that at the three way valve so that 100% of the return water goes to the pool returns (no spillway). But either way I have some flexibility.

Thanks!!


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[VladSI]

I get what you're saying but I would love to see some pictures too!

Pics follow. Keep in mind that what I did was just a crude test that I never took any further since it worked so well. It can be done much shorter and neater without the street elbow.

Important note if you end up doing this - while extending the air line just past the eyeball creates suction, if the line is behind the eyeball then it's the opposite. Pressure will push water up through the air line so I always keep the other end of the line pointed down into my skimmer just in case.

Beyond just the aeration benefit, the kids love standing in front of all the bubbles.

Bubbles breaking the surface:

Closeup:

 

[easttn]

Clever idea VladSI. If you turn the elbow away from the skimmer, it will create a circular current around the pool. I made something like that but I didnt have aeration in mind but I can turn it upwards where it pumps the water out of the pool water and aerates it that way. Im sure the kids wouldnt like that as much though.



Sunny Optimism you could get some of those flying carp and put in there and aerate. What about jets under the water where they shoot up out of the water like the casino in Las Vegas? Just another idea to keep your gears rolling.