any way to control pH better?

[Furbabyvet]

Hi everyone. My pool water balance situation has improved greatly since I started BBB about 2 months ago. I took a water sample to the pool store(yeah, the one that messed me up so badly in the first place!) to cross check my numbers and the 20 year old slacker working there said I got an A+. Yea, me and yea, poolforum.com . I didn't bother to tell him it was no thanks to his advice!

My numbers are approximately:
FC 5
CC 0-0.5
pH 7.7 today and rising quickly
CH 260
TA 80-90ish
CYA 40ish
Borates 40-50 ppm
temp. is 84-86 F
sorry for ambiguous #s but I have a hard time discerning the test result at times.

Anyway, I am happy with the way things are going except for two things. One is that there is still a very scant growth of green algae just above the waterline mostly on the "shady" side of the pool. It's only in a few places, not the entire pool. Raising water level an inch, shocking and scrubbing haven't made much impact on it. I've also tried adding polyquat 60, phosfree, and have now added borates to somewhere between 40-50 ppm. The algae is still there.

The other problem is that my pH keeps going up to 8 or greater, no matter what I do. We do have hard water in this area of AZ, but I was really hoping the borates would help slow down acid demand. The way it goes right now, I would need to add acid 2-4 times per week to keep it below 8.

Any ideas on either of these topics? Sorry if I posted in the wrong section!

Tabitha

[PoolDoc]

Hey Tabitha;

You'd gotten two earlier responses, from CarlD and Waterbear, that were sort of going at cross-purposes, so I'm jumping in here. I moved those posts to the China Shop for now. They are in the "Algae, TA or what" thread.

As I understand it -- please correct me if I'm misunderstanding -- you have two problems, one urgent and one longer term or chronic.

The urgent problem is the algae. If it gets away from you, you'll have serious problems, so we probably need to get that under control ASAP. More chlorine is the solution, at least right now.

The chronic or longer term problem is a continuing rise in pH. This problem may contribute to your algae problem, since chlorine tends to be less and less effective as the pH rises. So, lowering your pH -- regardless of how why it keeps going up -- is probably the next thing to do, after you get your chlorine level up.

So, let's do this.

1. Raise your chlorine level to 15 ppm, and then keep it above 10 ppm till the algae is gone.
2. Add enough acid to lower your pH to 7.2 or so -- but NOT all at once. If you know how to handle muriatic acid (no splashes, wear glasses, use gloves, don't breath the fumes) it's cheapest and best for your pool.
3. Don't try to fix anything else, till the algae is gone.
4. BUT, do collect the info we need to see if we can tell what's going on with your pH.

Regarding doses, I don't see any indication of pool size, but if you post gallons, we can figure doses or show you how.

If you're not doing so, make sure your pump is running 24/7, till the algae is gone.

As far is information goes, please do all the following (but take care of the chlorine and pH first):

1. Post pool gallons, typical timer 'ON' hours, filter type.
2. Tell us what sort of chemicals you are normally using (labels, chemical ingredient)
3. Tell us what's been happening with your TA -- has it always been this low, or has it been going down lately?
4. Test your FILL water for pH, chlorine, Alk, Calc, and post those results.
5. Tell us if there is anything connected to your pool that would aerate the water (fountain, waterfall, spillover edge, attached spa, air jet, etc.)

And, let us know you have a problem with any of this.

Good luck!

Ben
"PoolDoc"

[Furbabyvet]

Hey, thanks a lot for the help.

1. Pebble Tech pool. 11,940 gallons. Sand filter. Pump runs 7 hr. during the night and 1 hr. during the afternoon.
2. I use 10% chlorine, 29% muriatic acid regularly. I have 2 trichlor pucks in my floater right now to help with chlorine and to add CYA. I have also added borax. As I mentioned, I’ve put in polyquat 60 a few times—once I put in a whole bottle, but then later just a few ounces per week. A month or so ago was the last time I added PhosFree just because we already had it from last year.
3. 6 weeks ago, the TA was 230. I followed the procedure outlined here to get it down so I could add borax.
4. FILL water pH 7.6, Cl 0.5, TA 110, CH 250.
5. There are no water features in the pool, although we have a “aerator” nozzle that can be turned on as needed. I only used this when trying to lower the TA.

My water test today:
FC 6, CC 0, pH 7.8, TA 90, CH 280, CYA 40, Bor. 40

I have the solar cover on and the water temp at 7:30 am is 83 F.

The algae is still there, although not as bright green as it has been at times. It is about 3/4 of an inch ABOVE the water line. Will I need to fill the pool more to affect this algae or will it get enough chlorine as is?

Two months ago, I fought off what I believe to have beeen mustard algae in the form of brown “dust” that had been there for over a year but I didn’t know what it was. There is no sign of the brown dust and the pool water is as clear as clear can be.

Tabitha

[PoolDoc]

FACT #1: I have the solar cover on and the water temp at 7:30 am is 83 F.

The algae is still there, although not as bright green as it has been at times.

FACT #2: It is about 3/4 of an inch ABOVE the water line.

Ok. I think I've got the picture.

As a general rule, when you are trying to fix anything with your water, your pool needs to be on 24/7. But, in your case, the problem is OUT of your pool, not IN it. And, since the chlorine is IN your pool, neither it, nor any algicide will do the trick.

Is your solar cover the type that you trim to fit? If it is, have you trimmed it to fit, so it ONLY floats on the water, and doesn't cover the edges at all?

PoolDoc

[Furbabyvet]

Ok. I think I've got the picture.

As a general rule, when you are trying to fix anything with your water, your pool needs to be on 24/7. But, in your case, the problem is OUT of your pool, not IN it. And, since the chlorine is IN your pool, neither it, nor any algicide will do the trick.

Is your solar cover the type that you trim to fit? If it is, have you trimmed it to fit, so it ONLY floats on the water, and doesn't cover the edges at all?

PoolDoc

I think I overstated the distance of the algae from the waterline. It's more like 1/4 inch above and it's in small patches, in the pits between the pebbles. It does seem to be wet in that area, though.

The solar cover is a trim-to-fit type that floats on the water. I only put it on yesterday, so it is definitely not the cause of the algae that's been there off and on for weeks.

I went ahead and brought the Cl. level up to about 18 ppm and the pH is somewhere around 7.4 and going down as I add a little acid at a time. The cover is still on-- should I take it off? Doesn't seem like it will affect what I'm trying to do.


Tabitha

[PoolDoc]

Hi Tabitha;

Be cautious about your pH. As your chlorine level goes above 10, your pH readings, if measured with phenol red drops, will be less and less accurate. At 18 ppm . . . unless you are using a calibrated pH meter, you really don't know what your pH is.

Regarding the algae -- are you saying that you have algae in the pits and rough places at the water line?

If so, lowering the water level, and using a 1:10 spray of polyquat will probably work. Just make sure you use a CLEAN sprayer, with no herbicide or pesticide residue.

Or, if you've got an old clean sprayer that you don't mind ruining, spraying with straight bleach, and then 'pressure washing' with a hose and nozzle and the re-spraying will probably work.

But, it depends on how deep the rough spots are: you can only kill algae you can reach!

Once the algae's gone we'll need to see what the situation is with your pH.

Ben
"PoolDoc"

[Ohm_Boy]

Pump runs 7 hr. during the night and 1 hr. during the afternoon.

I'm gonna jump in here and reinforce that your pump needs to be circulating 24/7 while you are trying to clear up algae. Lack of circulation can make algae VERY hard to get rid of.

[Furbabyvet]

Hi Tabitha;

Be cautious about your pH. As your chlorine level goes above 10, your pH readings, if measured with phenol red drops, will be less and less accurate. At 18 ppm . . . unless you are using a calibrated pH meter, you really don't know what your pH is.

Regarding the algae -- are you saying that you have algae in the pits and rough places at the water line?

If so, lowering the water level, and using a 1:10 spray of polyquat will probably work. Just make sure you use a CLEAN sprayer, with no herbicide or pesticide residue.

Or, if you've got an old clean sprayer that you don't mind ruining, spraying with straight bleach, and then 'pressure washing' with a hose and nozzle and the re-spraying will probably work.

But, it depends on how deep the rough spots are: you can only kill algae you can reach!

Once the algae's gone we'll need to see what the situation is with your pH.

Ben
"PoolDoc"

OK, I'm gonna leave the pH alone for now, then.

Yes, the algae is in the very shallow pits (maybe 1/16 of an inch deep or less) that exist just above the waterline where calcium has built up and is rough because of the pebble tech finish.

I thought about spraying/scrubbing with bleach, but wondered why the stuff is there in the first place??? It is about 105 degrees here today and very low humidity. I've kept the chlorine levels in the range recommended her for my CYA levels. Why the heck are these little splotches of algae hanging on? I am hoping this round of shocking will kill it once and for all.

Back to the original question: any ideas about why my pH level goes up so fast? I've been taking it down around 7.6 but it is up to 8.0 within 3-5 days. The fill water is around 7.6, so I am not sure what's going on. Is it the relatively higher chlorine levels (not shock level) making it test higher than it really is?

Thanks!

[Furbabyvet]

I took some photographs:
http://www.flickr.com/photos/40043936@N04/?saved=1

[PoolDoc]

Some forms of algae seem to be able to create something like 'roots' into porous plaster and concrete surfaces. If you've got pits, you've probably got porous plaster. Once those forms of algae are established, killing the visible algae is sort of like mowing crab grass. You STILL haven't got the roots.

Unfortunately, there are no 'herbicides' for algae that will reach into the roots.

Once a penetrating algae is established, management is more a matter of control, rather than eradication.

You could do something like raising the water level to completely cover the algae, and then raising your chlorine level to 50+ ppm (no misprint - I mean "50") and holding it there for a week or so. That might kill all the algae. Or, it might not.

You can acid wash, which may remove the algae, but at the price of making your plaster even MORE porous than before, and thus more susceptible to NEW algae.

You can coat the pool with epoxy paint, which algae can't easily penetrate or grow on.

But, for this season, the practical think is control, not eradication.


Regarding pH, the short answer is, "I don't know why your pH keeps drifting up".

There are many possible factors. If you aren't using a kit with Taylor based reagents, sometimes as little as 3 ppm can mess up readings. But, that wouldn't cause a apparent rise, unless you raised your chlorine too.

If your pool is relatively new, changes in the plaster can cause changes in pH.

Or maybe, if you are using something besides trichlor tabs (which are acid) but have gotten a hold of some calcium hypochlorite tabs, that can raise pH.

Or something else.

I can observe that, in my experience with multiple large commercial pools managed with sodium hypochlorite (bleach) feed systems, I universally found that bleach fed pools 'wanted' to be at a pH of 7.6 or higher. I have no analytical explanation for this. But I can tell you that I discovered that if I let the pH float upwards, it usually -- but not always -- stopped before 8.0. I also found that if I operated the pools between 7.6 and 8.0 it took FAR less acid, than if I tried to operate the same pool between 7. 2 and 7.6. (Note to Chem Geek: yes, I tried it both ways on the SAME pools )

I never tried to mix trichlor and bleach -- not sure why you'd do that -- but regardless, you may find that your pool has some point below 8.0 where it will 'rest' or you may find that if you operate in the 7.6 - 7.8 range, it will continue to require acid additions, but only small ones.

If you run at higher pH, you'll need to compensate by running slightly higher levels of chlorine.

On another related note: buffering has to do with how difficult it is to change the pH of a solution (your pool water in this case). Highly buffered water has highly stable pH . . . . IF the buffer in question is effective at that pH level.

Most buffers have ranges over which they are effective, and other ranges over which they are not so effective. Cyanuric acid is an effective buffer at LOW pool pH levels, below 7.4 as I recall. Borax is an effective buffer at HIGH pH levels, above 8.0, I think. Total alkalinity tests measure how much buffer you have, but not which levels it's effective at.

This is important, because if you have drifting pH levels like you do, it's your pool's buffer system that determines how hard you'll have to work to maintain your pH level. Absent aeration, sodium bicarbonate is an effective buffer in the 7.0 - 8.0 range where your pool lives. A pool with an effective bicarbonate based "Total Alkalinity" will require larger doses of acid, added less frequently, compared to a pool without that bicarbonate based buffer.

More or less, a well buffered pool will require that you adjust your pH less frequently than a poorly buffered pool. It won't really decrease how much acid you need, but it will change how often you have to add it!

This doesn't matter on a pool with a stable pH -- if the pH is not moving, you don't need something (an effective buffer) to keep it from moving fast. But on your pool, it does matter.

For that reason, I wouldn't recommend trying to replace your bicarbonate buffer system (effective in the pool pH range) with a borate buffer system (not so effective in the pool pH range). But it's up to you. You can run the pool successfully either way.

Best wishes,

Ben