Trying to solve pH rise -- could cavitation cause aeration?

[lalittle]

I have a constant rise in pH such that I'm having to put acid doses in the pool at least a couple times a week. I'm using a combination of pucks and liquid chlorine -- just enough pucks to keep things "leveled out" and to reduce the amount of times I have to add liquid Cl. The pH is a little bit worse in the summer, which makes sense since I add more liquid Cl, which adds to the rise in pH, but even now in the winter I'm still adding acid twice a week even though my liquid Cl additions are FAR less frequent. Given that the plaster is no longer "new" (two to three years old at this point) the only thing I can think of that would make the pH rise so fast is aeration.

I don't have any water features, but I see a constant fog of tiny bubbles coming out of my inlet jets, indicating that air is getting into the system somewhere. I had a leak detection guy come over an check for leaks by pressurizing everything, and after his tests he concluded that I did not have any leaks. I'm using a Kreepy Krauly for the cleaner, which somehow pulls in a little air as evidenced by a constant bubble in the leaf trap that comes back even if I remove it. At first I thought that it was just hose leaks causing the air in the line, but I put on new hose sections and it continued to happen. After thoroughly checking the hose, I started to wonder if the cavitation could cause air to appear in the line, which could then cause pH rise. I always thought that cavitation bubbles would instantly disappear (i.e. that cavitaiton couldn't cause air bubbles coming out the jets), but I'm not sure how everything works together in this situation. If cavitation could lead to pH rise, I wonder if the pump itself could be causing enough cavitation to explain the situation. It's a VERY old pump that had the impeller replaced by the previous owner, but I think it was done on-the-cheap, so it wouldn't surprise me if it could be causing problems.

My questions, therefore, are:

1) Does the fog of little bubbles indicate enough aeration to make the pH rise? In other words, how much aeration causes how much rise, and does the evidence I'm seeing indicate enough aeration to see such a noticeable rise in pH?

2) Could cavitation alone (either in the KK system, the pump or both) cause the air that I see coming out of the jets?

3) Could enough cavitation, by itself, cause pH rise, and could the pump do this?

4) Does the air in the leaf trap (in-line with the Kreepy Krauly hose) indicate a hose leak, or could cavitation explain this.

Are there any other questions that I should be asking here? I'd really like to figure the situation out after discovering that many people only have to add acid every few weeks or even months. Even people with salt water Cl generators don't seem to need as much acid as I do. I feel like there is a solution to this -- I just haven't been able to find it yet.

Thanks for any help with this,

Larry

approx. 21K gallons
FC 7
CC negligible (.5 or less)
pH (target) 7.4 - 7.5
TA 70
CYA 70

 

[Richard320]

Re: Trying to solve pH rise -- could cavitation cause aerati

How old is the pool? If it's still in its first year, you will use a lot of acid.

 

[y_not]

Re: Trying to solve pH rise -- could cavitation cause aerati

Really, as far as I have learned. You have to have a major blockage in the lines on the suction side in order to have any sort of meaningful cavitation occur. That's the only time I have ever seen it anyway. Something stuck in the suction pipe, junk in a grate/basket somewhere, etc..
But I'm not an expert on the subject.

However, if you have "tiny bubbles" and lots of them coming out your returns. You have a leak somewhere, despite what "leak guy" says.
You're getting aeration in the water, which is causing CO2 outgassing, thus raising your pH.
You don't state how much of a pH rise you're seeing though.

Just to clarify, you state "inlet jets" in your original post when you are referring to the bubbles coming out.
I presume you are referring to the "return jets", or "eyeballs" where the water pumped out of the pool and sent through your filter, then returns to your pool. (IE. You stick your hand in the pool in front of them, with pump running and you feel a pressurized water stream.) Correct?
This is the "pressure side" of the system, as water is being pumped back to the pool, thus under pressure from your pool pump's circulation action via its impeller.
The "suction side" is the inlet, where water gets sucked out of your pool by the pump. Either from the skimmer(s), main drain(s), or a combination thereof.
This is the "vacuum side" and is typically where air is introduced into the system, clear up to and including the pump.

You absolutely must find the leak and fix it.
Some things to check, by no means exhaustive.

- Do you see air in the pump basket?
- Do you bleed your filter?
- Is the water line at your deck side skimmer appropriate?
- Are you seeing a "vortex" in your deck skimmer?
If so, fix it with a rock in the bottom, or by fixing your skimmer's weir door.
- Is the lid of your pump basket on snug, not wrenched, but just snug and lubed with silicon grease?
- If you have that option, do you still see bubbles if you put your filter in bypass mode, as well as shutting off any water features?
- What happens if you shut down and disconnect the Kreepy Krauly system? Does pH still rise, do the bubbles go away?

Lastly, pucks cause your pH to drop as they're acidic.
Bleach does not raise your pH, it is pH neutral. It raises it temporarily since it's alkaline, but the consumption process of the hypochlorous acid is, as it says an acidic process. So it drops the pH back down.
You'd literally just about have to check your pH obsessively over the course of an hour or so after 1st adding bleach to the pool, in order to see the change.
For all practical and real purposes, the pH doesn't change in the end.

You're using more acid in the summer, more than likely because you are either using fewer pucks, thus less acid being added by those. Or, you are running your pump more, thus aerating the water more and causing a higher pH rise. Also, swimming in the pool, splashing, diving, etc.. Those all create tiny bubbles that raise your pH.

 

[JohnT]

Re: Trying to solve pH rise -- could cavitation cause aerati

Often a suction leak won't leak under pressure. What size is your pump and what kind of plumbing do you have? What is your pool surface, and how old is it?

Liquid chlorine doesn't cause a pH rise, but your use of pucks has pushed your CYA into the region where you want to quit using the pucks.

 

[UN1017]

Re: Trying to solve pH rise -- could cavitation cause aerati

I have a constant rise in pH such that I'm having to put acid doses in the pool at least a couple times a week.

How much and what concentration of acid are we talking here?

1) Does the fog of little bubbles indicate enough aeration to make the pH rise? In other words, how much aeration causes how much rise, and does the evidence I'm seeing indicate enough aeration to see such a noticeable rise in pH?

Absolutely. An SWG doesn't generate a large amount of bubbles and we all know that pH is affected. There is no rule of thumb. Each pool is different.

2) Could cavitation alone (either in the KK system, the pump or both) cause the air that I see coming out of the jets?

Maybe. Remember, cavitation bubbles are created when the water undergoes a considerable decrease then an increase in pressure (i.e. constrictions or elevation changes). The bubbles produced are from gases already in the water. Does that effect pH? Does the gas redissolve? I don't know. That's above my pay grade.

3) Could enough cavitation, by itself, cause pH rise, and could the pump do this?

See above

4) Does the air in the leaf trap (in-line with the Kreepy Krauly hose) indicate a hose leak, or could cavitation explain this.

Could be both.

I'd really like to figure the situation out after discovering that many people only have to add acid every few weeks or even months.

May never happen and that's ok. It doesn't mean something is wrong with your pool. I would say that most people here add acid at least once a week. Myself included.

We don't want to make it too easy....that would take all the fun out of it.

 

[UnderWaterVanya]

Re: Trying to solve pH rise -- could cavitation cause aerati

Good reading on the topic of cavitation.

http://www.mcnallyinstitute.com/01-html/1-3.html



Sent via Tapatalk...

 

[lalittle]

Re: Trying to solve pH rise -- could cavitation cause aerati

Thanks for the responses.

With regard to "how much" the pH is rising, I'm adding a "dose" of acid (i.e. enough to bring the pH down one "step" on the Taylor color scale, which is 0.2) 2 to 3 times a week. I can reduce the number of times I add acid by letting the pH go higher in between adding it, but I still feel like I'd adding more doses than average. Is this not the case? Everyone I talk to around here says that they "rarely" have to add any acid -- I'm just going by that.

I did use the wrong terminology above -- I meant "return jets" not "inlet jets." I'll fix that.

I'm not sure I understand what to do regarding the leak detection tests. I thought that this is what you do to CONFIRM whether or not you have a leak when you suspect you may have one. If these tests are not conclusive, how do you ever confirm a leak? In other words, how do I attack a leak problem if the controlled pressure tests are not reliable? How would I ever find the leak? The leak detection guy seemed totally convinced that I did not have a leak -- is this really not reliable?

I did check all the "normal" causes of air leaks listed above -- i.e. skimmer (which is at the correct level with regard to the water line), pump lid, etc. I also added silicone to the seals on the pump basket lid and filter. I do have some pressure side leaks at the pump, but water is coming OUT of these leaks, so I don't think air is getting in. I'll do some tests without the Kreepy Krauly tomorrow to see if I still get the tiny bubbles. I don't have a "bypass" mode on my filter. I do get a vortex in my skimmer when the KK is not hooked up, but as far as I know, it's normal. Unfortunately, the previous owners plugged the pools bottom drain (they said that put concrete in it), so it creates a circulation problem when running the pump without the KK since all the water gets pulled out the single skimmer.

Note that the pool was resurfaced about 3 years ago, which I believe is long enough to "stabilize" and not cause any pH rise.

I'll report back with any new information I find.

Thanks again,

Larry

PS. The pool is around 21K gallons. I don't understand what is meant by "what kind of plumbing" I have. It's 2" PVC for the most part -- is that what was meant?