Re: any way to control pH better?
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
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Originally Posted by PoolDoc
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