any way to control pH better?

[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"

[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

[PoolDoc]

Just saw the photos -- so-called black algae.

And, with an eroded pebble finish like that, you've got a long term maintenance issue.

Could you mail larger versions of those photos to me at poolforum AT gmail DOT com?

I'd like to edit them, comment on them, and repost them here. I can explain a bit more of how and why, and what to do, if you do (BLACKMAIL, here! )

Ben

[dhanger]

PoolDoc-

I just wanted to comment something about the surface, I'm in AZ too, and it seems to be a real popular finish here, the PebbleTec. It's not eroded plaster, as you seem to think (I don't mean to insult your intelligence if you already know what I'm talking about), which is a small pebble inlay with concrete or grout as a binder surrounding it. The difference in depth between the top of the pebbles to the binder is no more than 1/32". I have no idea whether that would affect your diagnosis or not, but I thought it might be helpful to clear that up.

Dan

By the way, I have the same issue regarding pH rising, in my 5 years with this pool, not once have I ever had to raise it, always lowering. Don't know if that has something to do with the water here, the environment, or what.

[PoolDoc]

No insult taken . . . I didn't actually think Pebbletec was eroded plaster, but I've seen pools with, hmmmh, shall we say raggedy edge finishes, so I didn't want to get too specific. The bottom line for me, when I'm posting here, is that I'm usually pretty conscious that I don't really know what the poster actually has on, or in, or around their pool.

In this case, seeing the pictures was really interesting. I hadn't realized that you'd get waterline deterioration of the interstitial filler in Pebbletec like his pictures show.

By the way, do you happen to know the actual chemical or mineral composition of the "pebbles" and of the filler?

PoolDoc

[waterbear]

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 have seen the same effect on customer's pools with SWGs and on the commercial pools with bleach feed systems also, and have discussed this before on different forums.



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.
At normal pool pH range most of the borate/boric acid buffer is in the form of boric acid and has a downward effect on pH when it starts to climb as opposed to the bicarbonate/carbonic acid buffer which causes ph to move toward 8.2

Just my 2 cents.

[Furbabyvet]

Another late update on the waterline algae problem. After using the BBB method all summer and attacking one more algae bloom (due to landscaping debris left in pool too long and my negligence), the waterline algae is completely gone. We did scrub with bleach, but I think it was just having balanced water over time that really fixed it.

I'm still amazed at how stable our pool has been using these simple concepts. Now that we have things under control, we're gonna try a SWCG to indulge my laziness even more. Ya'll are great. Thanks a million!

Tabitha