PH Questions

[Charlie]

Just checked it at 5:30pm my time, and the pH is now 7.4 and the TA is 110. From these numbers, it looks like it will take me ~2 weeks ± a day or to in order to hit my target of 70.

[chem geek]

Try pointing all of your returns upward. You could also be a little more aggressive with the acid getting closer to 7.0 without overshooting (kind of the color between 7.0 and 7.2). It is a slow process, but I don't think it will take quite as long as you think.

[Charlie]

Just an update:
pH: 7.2
TA: 80
CYA: 50 (was 40 yesterday)

I added stabilizer yesterday, but I probably need to let it go for a few more days before I can an accurate number?

Just a little bit more to get to a TA of 70.

[aylad]

If you added it through a sock hung in front of a return, then I would give it at least 2-3 more days before you get the accurate level.

Janet

[Charlie]

Finally got my TA to 70. My pH is currently 7.2. From all this daily testing, it looks like my pH goes up ~0.1-0.2 each day. Just need to bring up my CYA to 80. Its currently at 60.

[chem geek]

The rate of pH rise will likely be faster at the lower pH so see what it does when it gets closer to 7.7. You may want to target a pH a little higher than 7.5 and not try and lower it below 7.5 in the future.

[Charlie]

With my levels getting closer to the recommended amount, I've created a spreadsheet to document the tests. Here is what I have, and let me know if these values are okay or not. I hope I'm close:

I've pasted the values in a Word Document for easier viewing:
http://mysite.verizon.net/res6ncxf/TEST.doc

[chem geek]

Your Minimum column has too low an FC (2) for the CYA level (60). For an SWG pool, it should be an FC of 3 for a CYA of 60. Basically, shoot for an FC that is a minimum of around 5% of the CYA level. This is lower than in Ben's chart used for manually dosed pools, but seems to work well for SWG pools.

You don't need to worry about the phosphate level. I've got 2000-3000 ppb phosphates in my pool and am able to control algae using chlorine alone (well, this year I also have borates in the pool, but I didn't before this year). You might consider using 50 ppm Borates in your pool since this helps to control pH rise, helps prevent scaling in the salt cell, and also inhibits algae growth.

Your minimum numbers are way too low when taken as a whole. The low pH, TA and CH combine to produce a saturation index of around -0.8 which would tend to dissolve the plaster in your pool. The ideal levels you listed have a saturation index of around -0.3 while the maximum levels have a saturation index of around +0.2. You should use The Pool Calculator to calculate the saturation index and try to target something close to zero or perhaps slightly below (i.e. -0.1 or -0.2 but not much lower) to lessen scaling in your salt cell.

Generally, to minimize the rate of pH rise you want your TA at around 80 ppm and your CYA at 80 ppm. That means your FC should be 4 ppm minimum and for decent water balance with salt at 3000 ppm your pH target should be around 7.7 and your CH at 300-500. If you target your pH at 7.6, then your CH should be 350-600.

Richard

[Charlie]

Thanks Richard for your review. That makes sense - the saturation index is what I should use to target minimum and maximum levels.

[chem geek]

Roughly speaking, one sets the CYA level according to the amount of sunlight protection they need, though usually not too high (with SWG pools, 80 ppm is OK if the FC is set at 4 ppm or higher). Then with the CYA level, this determines your FC target.

You set your TA appropriately for your source of chlorine. For hypochlorite sources, you set your TA on the low side, usually around 80 ppm but sometimes lower if the pH tends to rise. The pH target is usually around 7.5, but for SWG pools where the pH tends to rise it could be 7.7. After all of these are set, then you add enough calcium to have the CH high enough to have the saturation index close to zero. So in an SWG pool, with its higher salt level and a tendency for the pH to rise, one may have a lower TA and a higher CH than in non-SWG pools.

Richard