Impact of rain on ph

[Ahultin]

For southern California, we had a biblical amount of rain yesterday which overflowed our pool. Pool level was already high from last weeks rain but yesterday's added at least 5" plus (level was even with top of coping so I don't know how much ran out overnight)
I last tested Friday and all was well but when I went out today the water color was off so I knew we had an issue. Ph this morning on my ph60 showed 9.01. It's never been that high since pool startup so as a backup I used the taylor test as well and it showed off the charts pink. The ch also dropped by at least 100ppm and salt dropped 200ppm from last test. The oddball was the cya which seems the same.
Before I go adding a ton of acid (83 ounces per pool math) I wanted to make sure these are normal impacts of rain ?

 

[JamesW]

TA before and after?

 

[Ahultin]

TA before and after?

Both 60

 

[JamesW]

Recalibrate the pH tester and check the pH with the liquid test kit.

If you have distilled water, test the pH and it should be close to 7.0.

It's unlikely that the rain raised the pH that much.

If the pH really went that high, the TA would have also gone up.

You can get loss of CO2 due to aeration, but the pH will not go over 8.3 with aeration.

Allow the pump to run for 24 hours and brush the pool to mix in the new water and allow the chemistry to equalize.

If the pH is still high after 24 hours, maybe add a little bit of acid.

 

[proavia]

Was the pump running for at least 30 minutes prior to pulling the water sample?
How far below the water surface was the sample taken?

 

[JamesW]

The ch also dropped by at least 100ppm

That seems unlikely.

Retest after 24 hours.

 

[JamesW]

Maybe leave out a plastic bucket or cup to catch some rain the next time it rains for testing purposes.

What is your fill water chemistry?

 

[Ahultin]

Was the pump running for at least 30 minutes prior to pulling the water sample?
How far below the water surface was the sample taken?

Pump runs 21hrs a day @1000rpm and had been running 2.5hrs at time of test. Sample was taken at elbow depth so @12"

 

[Ahultin]

Maybe leave out a plastic bucket or cup to catch some rain the next time it rains for testing purposes.

What is your fill water chemistry?

Fill water was tested @5months ago at ta of 110 and ch of 200.
I have a rain barrel that catches roof runoff, I'll pull water from there now and test.

 

[Ahultin]

Recalibrate the pH tester and check the pH with the liquid test kit.

If you have distilled water, test the pH and it should be close to 7.0.

It's unlikely that the rain raised the pH that much.

If the pH really went that high, the TA would have also gone up.

You can get loss of CO2 due to aeration, but the pH will not go over 8.3 with aeration.

Allow the pump to run for 24 hours and brush the pool to mix in the new water and allow the chemistry to equalize.

If the pH is still high after 24 hours, maybe add a little bit of acid.

Recalibrate the pH tester and check the pH with the liquid test kit.

If you have distilled water, test the pH and it should be close to 7.0.

It's unlikely that the rain raised the pH that much.

If the pH really went that high, the TA would have also gone up.

You can get loss of CO2 due to aeration, but the pH will not go over 8.3 with aeration.

Allow the pump to run for 24 hours and brush the pool to mix in the new water and allow the chemistry to equalize.

If the pH is still high after 24 hours, maybe add a little bit of acid.

Tested distilled at 7.03
Recalibrated ph60
Pool water still tested 9.01/9.02
Spa water interesting enough tested 8.26 (my spillway has been running only 15m per day at 7pm unless I run it since upgraded intellicenter to 2.06 so it was off for the overnight rain)

Pump currently running on high with spillway active
Brushed and vacuumed

 

[JamesW]

OK, seems odd to get that high of a pH.

If it is still high after 24 hours maybe add a little bit of acid but be conservative.

 

[Ahultin]

Fill water was tested @5months ago at ta of 110 and ch of 200.
I have a rain barrel that catches roof runoff, I'll pull water from there now and test.

Well...that was not the expected result.
Qualifier - rain barrel is a repurposed used wine barrel, rain water is collected at the top from the gutters. There is an overflow which was spilling during last night's rain. Hose bib is at the bottom of the barrel. There is no way to mix what's in there so collected water is a sum of the last few weeks of rain. I discharged from the hose bib for one minute then collected.
Ph 6.80
Ta 40
Ch 50
Fc 0

 

[JamesW]

The pH might be rising from plaster dissolving or scale dissolving, but that would raise the TA and the CH by equal amounts.

Your numbers for pH and CH change are puzzling.

 

[Ahultin]

Fill water test today
Ph 7.6
Fc .5
Ta 100
Ch 250

 

[JoyfulNoise]

If the rainwater overflowed your pool, then the uppermost layers of the pool water would be exposed to the ground and decking around your pool. There could easily be major changes in pH when water contacts soil or decking materials. Rain water can vary quite a bit in pH but will often be slightly acidic and very “corrosive” to anything it contacts. This is why your rain barrel has low pH but high levels of TA and CH - it picked that up from the gutters.

I suggest draining the pool down to a normal level (middle of the tile line) and then letting the pumps run for 24 hours before testing and adding chemicals. Rain water will float on pool water and can take significant amounts of time to homogenize.

 

[jmastron]

Agree that it isn't normally the effect of rain -- we are getting similar large amounts of rain here in NorCal (probably from some of the same clouds ), and my pH is lower than it was before. Coincidentally, out of curiousity I tested the rainwater yesterday, and it was fairly acidic (low 7s/high 6s). Now, this was scooped from a puddle on the brick patio so that could affect things, but I've never seen rain raise the pool pH. It's definitely possible that other things washed in, but I'd be cautious about trusting the pH meter for absolute readings that high even after calibration.

I agree with the idea of getting down to a normal water level (at least fully on the tile line; I'm letting mine stay a little high as we may be heading into a dryer period finally soon) with pump running for a day and testing again. I would use the drop test along with the meter, and break up the addition to be safe. If the drop test says you're over 8.0 you don't know by how much so you add just enough acid to go from 8.0->7.2 (or higher), wait an hour or so, and test again with the drops and meter. Repeat until it's in the normal range, so you don't overshoot.

I just put out a container to collect some fresh rainwater, will test it when I have enough.

 

[JoyfulNoise]

Rain water forms when the air temperature reaches the dew point temperature at a given altitude and atmospheric pressure. That’s the thermodynamics of it and it represent the equilibrium conditions necessary for liquid water formation. In reality, the kinetics of water formation process requires more energy than that and a nucleation site (typically dust or some suspended chemicals element) is needed to reduce the energy barrier of the formation process. So, what that means is that rain water is pure water PLUS stuff that it absorbs in the atmosphere as it falls. Nitrates and sulfates are present in the atmosphere and both are useful for seeding rain formation. They also tend to lower the pH of rainwater. Rain water will also absorb CO2 from the atmosphere as it falls thus becoming more acidic. If you can capture rain in a non-reactive, clean container (quarts glass works well), you will typically find it’s pH down around 5.5-6.5 and an alkalinity of about 20ppm or so. If you had a way of measuring nitrates or sulfates, you might find trace quantities of those two compounds as well. The moment rain water contacts the ground or any other surface material, it will quickly leach minerals (sodium, calcium, potassium, magnesium, etc) from them as well as any carbonates or chlorides present. Iron is quickly leached as well. Most household glassware is made from soda-lime glass or borosilicate glass and is not “clean” enough to capture pure rain water. Even quartzware needs to be properly cleaned to avoid trace amounts of sodium from being leached out of it. Pure water can even dissolve a certain amount of silica (SiO2) into solution from the glass surface.

Water is truly the ultimate solvent … just ask the Grand Canyon.

 

[kul]

That seems unlikely.

Retest after 24 hours.

I agree with this regarding the Calcium. I have drained my pool about 4 times due to rain overfill and checked my CH after the third time and it only went down about 25-50 (feel free to check my logs). This aligns to the pool math calculator. Strange that yours would go down by 100 if you haven’t actually removed any water. Even with overflow that’s surprising.

 

[Ahultin]

I noticed a section of my raised bond beam that is wet and dripping. It is quite possible that what was also coming over in this corner at the height of the rainfall although I checked our camera history and don't see any but that corner is also not illuminated so I don't have the best shot. The lot above ours is about 4 acres of planted field so it would not be beyond the realm of possibility that the runoff has a high fertilizer/ nitrogen content which I understand to be basic.
For now, pool has been drained down to normal level and Intelliph is still injecting regular acid. I also dug out some of the debris in the upper brow ditch to slow runoff coming down the outside edge of the slide as well as dug down the bottom corner so whatever does come down hopefully makes it to the French drain. I will test again tomorrow

 

[Ahultin]

Pool pH still way out of whack today. I did end up adding some acid yesterday as well as ran the spillover for about an hour to mix the pool and spa water which netted 7.8
I also left the overflow drain open so pool level stayed relatively static (I presume this results in less "mixing" of the rainwater?)
This morning test results are :
Rain caught in plastic bowl:
Ph 6.23
Ta ~10 (bright red with 1 drop r009)
Ch ~25 (barely red to bright blue with 1 drop
Puddle runoff from hillside
Ph 7.16
Ta 50
Ch 225

Pool
Ph 8.51
Ta 60
Ch 325
Salt 2800
Fc 9
Cc .5

Spa
Ph 7.99