Old Pool pH Always Up

[sbcpool]

When I purchased this home the TA was testing at 100 and the pH was above the test kit range. It took two gallons of MA to get it down to about 7.5. I discovered shortly after that the pH would bounce right back up to 8.2 after a couple of days. I'd add another gallon of MA to get to 7.5 and repeat the process for a couple of weeks. My TA is now down to 40 and the pH still keeps climbing right back to 8.2 a couple of days after adding MA.

The plaster is about 35 years old, so I don't think it's contributing.

Any ideas?

 

[duraleigh]

Do you have water features that cause aeration?

 

[jblizzle]

Do you have a lot of overflow from the spa to the pool? Or other water features that would cause aeration?
SWG?

 

[sbcpool]

Yes. The way the filtration works there will always be a lot of aeration, especially the water flowing from the spa to the pool. There's no way to shut it down completely.

 

[Richard320]

Mine settled down once I got the TA down to 60-70. I also throttled back on the three way valve to my spa, so it gets maybe 15% of the return flow and none of the suction. There's a narrow spillway about a foot wide and it is only about ½" deep when it's spilling.

I know from experience that for every inch of refill water I add, I need to add 2 cups of acid. Have you seen a correlation between topping off the water and acid demand? Do you have an autofill and an overflow? You could be constantly feeding fresh alkalinity into the pool that way and not realize it.

 

[sbcpool]

The pool is plumbed so awesomely. If you turn the three way all the way to the spa side, of course all the filter output goes to the spa. If you turn it to the middle the output is split between the pool and the spa. If you turn it all the way to the pool it is split between the pool and the spa, but comes out of different returns in the spa. In other words, you can't stop the spa from flowing into the pool.

I don't have an autofill and so far have only* been needing to add about 450 gallons a week to keep the pool topped off. I don't think even 450 gallons of Dead Sea water could raise the pH of a 20,000 gallon pool that much.

* Only is relative. 450 gallons a week is more water than my entire 4-person household used before moving to this house.

 

[jblizzle]

Post up a picture of your plumbing. Might be simple to add a valve to stop the flow to the spa ... usually there is a shutoff valve on the spa make-up line so that you can set the amount of water to the spa when in pool mode.

 

[sbcpool]

The valve on the left controls suction and the valve on the right is the return. As you can see, the returns go straight into the ground after the valve, so there is no other valve.

 

[jblizzle]

Isn't there a Tee at the bottom of the left return line? Where does that go?
Is the pool return on the left and the spa return on the right?
If so, I would guess that smaller line is what is feeding the spa.

 

[chiefwej]

Is there a drain in the spa on the suction side? Just wondering if you could balance the flow to the spa by drawing water from the spa on the suction side.

 

[sbcpool]

Isn't there a Tee at the bottom of the left return line? Where does that go?

I'm fairly certain it's capped off, but I'll check again when I get home. There are a couple of former plumbing lines on the pad that are just cut off at concrete level and left open or capped. I imagine they've had plumbing issues in the past as some of the current lines do not work.

Is the pool return on the left and the spa return on the right?

Yes.

If so, I would guess that smaller line is what is feeding the spa.

The smaller line is coming from the filter. The filter is old and only has 1.5" plumbing.

- - - Updated - - -

Is there a drain in the spa on the suction side? Just wondering if you could balance the flow to the spa by drawing water from the spa on the suction side.

That's something I hadn't considered. I may be able to get away with that. I still can't figure out the root cause, though. Water "wants" to be pH 7.0 in the absence of hydroxide ions. Where are they coming from?

 

[sbcpool]

OK. I double-checked. That tee goes nowhere. See photo. I did manage to balance the spa intake so that no water was spilling into the pool. The pH was 8.2+ again yesterday, so I added about 35 oz. of 14.5% MA per pool calculator (TA 40) to get 7.5. I'll check this evening and then cross my fingers that it stays stable.

 

[jblizzle]

Trying to balance spa suction is not recommended. A change in the floor characteristics, like the pool skimmer getting dirty could end up draining your spa and pulling in air.

 

[sbcpool]

Unfortunately I have no other way to stop the spa from overflowing to the pool. It's not a waterfall or anything, but just a "tunnel" between the two, but the water from the spa ripples across the surface of the pool for a good 5 - 10 feet. That's a lot of aeration. I can't see dumping gallons of MA and hundreds of pounds of baking soda every year into the pool as being sane or reasonable. There has to be a better way.

 

[jblizzle]

The picture shows both the spa and pool returns open ... I see you have tried turning that valve and closing the spa side and still go flow.

What does the "tunnel" look like?

A little rippling is not that much aeration compared to a spill over water fall.

 

[sbcpool]

It looks almost exactly like a skimmer opening, but just a straight-through to the spa. The surface rippling is pretty strong. It looks like the wake from a boat with secondary waves.

Like this, but without the foam and not as large of course.

 

[jblizzle]

Hmmm ... odd that they would have the split from the pool to these other spa returns hidden underground with no control over them.

 

[sbcpool]

All of this is assuming the spa overflow is the source of my rising pH. I've been wondering if the MA has been chewing away at the abundant calcium deposits and that's where the acidity is going. I have to wait to test until my wife can help since being red/green colorblind makes the calcium test impossible (although the TA test is no issue).

 

[jblizzle]

Interesting that you can not see the CH test turn from pink to blue, but can see the TA test turn from green to pink.

 

[sbcpool]

As far as splitting the spa output, it's not really split. There's the returns that are plumbed from the spa return line and still other returns in the spa plumbed to the pool return.

Interesting that you can not see the CH test turn from pink to blue, but can see the TA test turn from green to pink.

It's because colorblindness is much more complicated than a simple "red/green" misnomer suggests. It all depends on the exact shade. You can experiment yourself with a couple of different free colorblindness simulator apps for you smart phone, or at Web sites like Vischeck: Home. It's always been odd to me that society will spend hundreds of billions of dollars to make sure that the 1.5% of people in wheelchairs can function independently, but we won't even take the time to print a color-coded map so that the 5% of the population who have impaired color vision can use them.

This is supposed to be a simulation of the calcium test when corrected to resemble how I would see them. I have no idea if it really is because they still look a little different. Are they nearly impossible to tell apart to you? I guess it doesn't help that I have a lot of copper and magnesium in my water screwing with this particular test.