using citric acid to remove metal stains...

[river-wear]

Thanks for the help, Evan. I'll doctor things up to get a better balance. Maybe I won't have to be adding acid quite as often if the water is buffered better. I do usually run the pool at a pH of 7.6. One question though - why so high on the CH?

You asked about the salt - I used one of PoolDoc's test kits for that. I think it's more accurate because when I was relying on the Autopilot last year (too lazy to test), the chlorine just didn't seem to keep up with demand and I had to put the SWCG on the highest power setting. Now, with the higher salt level I put it back down to the "normal" power setting (there are three) and the water has been clean & clear all summer. In any case, it's in operating range as you pointed out; it just seems to run better/more efficiently now. I also read that the Autopilot will read the salt levels with varying accuracy depending on the temperature of the water.

[waterbear]

Thanks for the help, Evan. I'll doctor things up to get a better balance. Maybe I won't have to be adding acid quite as often if the water is buffered better. I do usually run the pool at a pH of 7.6. One question though - why so high on the CH?
To keep the water balanced with the other parameters I gave you since you have a plaster/fiberglass pool. I kept your Saturation Index within 'range' with a pH range up to 8.0 so you don't develop scaling conditions and there is some evidence higher CH can help prevent fiberglass staining. The parameters I gave you for CYA, pH and TA are to minimize your acid demand.
You asked about the salt - I used one of PoolDoc's test kits for that. I think it's more accurate because when I was relying on the Autopilot last year (too lazy to test
I am going to assume this includes all tests including pH and CYA, correct?), the chlorine just didn't seem to keep up with demand (sounds like low CYA) and I had to put the SWCG on the highest power setting. Now, with the higher salt level I put it back down to the "normal" power setting (there are three) and the water has been clean & clear all summer.
Did you raise your CYA?
In any case, it's in operating range as you pointed out; it just seems to run better/more efficiently now. I also read that the Autopilot will read the salt levels with varying accuracy depending on the temperature of the water.

Understand that the Autopilot is meaureing conductivity and not chloride ions like a chemical test. While the two are usually in the ball park they are not the same and for the sake of a SWG operation it's interested in the conductivity of the water and nothing more.
(Poolsean, Please correct me if I am wrong on any of this)
As far as the PoolPilot power settings, these should have nothing to do with salt level UNLESS you are running your salt way too low or unless your cell is fouled with calcium deposits and needs cleaning and cannot generate enough chlorine. The salt sensor in the AutoPilot is temperature corrected, which is why your cell output seems to fluctuate somewhat with temperature. My question for you was where was your CYA when you had to run at the higher power level? Low CYA is more likely to cause needed to bump the power than any other reason. Evan now at 50 ppm your CYA is too low and you should raise it to 80 ppm. This will translate into lower output setting which will translate into less CO2 outgassing which translates into more stable pH. The lower TA is also to lessen the outgassing of CO2. Ditto for not allowing the pH below 7.6 in normal operation. The lower you put the pH the faster you outgas CO2 and the faster pH rises.

[river-wear]

Interesting stuff, thank you!

Today I picked up the baking soda for raising TA, and will get the CYA and calcium tomorrow.

No, I wasn't too lazy to test other things last year. I just skipped the salt test. Last year I ran the Autopilot with it reading 2800-3000ppm (now it's 20% higher).

My CYA is about the same as it was last year. I added some this spring because the pool overflowed with a bit with the winter rains, diluting it. That's why I had to add quite a lot of salt too. In any case, I will bring it up to the recommended levels.

[waterbear]

Be sure to only raise the TA by 10 ppm. You want to keep it at 70. (You could also just leave it at 60 ppm for now and if and when it drops below bring it back to 70 ppm and not higher! )
You have never said how big you pool is so I cannot help you with dosing info but for everh 1000 gallons a SCANT 1/4 cup of baking soda will be in the ballpark to raise the TA by 10 ppm.
I would put in 3/4 of the amount you need over a period of several days--a small amount each day (because you just did the stain removal and you don't want pH to jump quickly lest the stains return., wait 24 hours after the last addition, adjust pH to 7.6 if it is higher (use your acid demand test if you have one)--If it's lower don't worry too much about it, wait another day your TA.
If it it still too low start adding the remaining 1/4 of the baking soda left over a few days and repeat the pH adjustment and testing.

I would not do this until you have finished with all the stain removal and your chlorine is holding properly.

[river-wear]

Pool size is in my signature - 27,000 gallons.

I only put in a one pound box of baking soda so far. (The pool calculator site says I'll need five.) I had to add water last night and didn't want to bring up the pH too quickly, just like you wrote. I will hold off until I can get in there with the Vitamin C tablets to finish off my stubborn stains. (And get the chlorine stable.)

I'll look for calcium hypochlorite at the pool store (my once-annual trip, I suppose) to try to hit two birds with one stone. I realize that more calcium will be needed than just what is in chlorine though.

[river-wear]

One more thing on the salt readings from the Autopilot vs. using a test kit. I had to look it up to make sure I hadn't "mis-remembered" that the reading will be affected by water temperature:

http://en.wikipedia.org/wiki/Electri...ure_dependence

My water is about 78-80 degrees now. I don't know off-hand what temp the SWG would have been calibrated at. I'm not too concerned about that since I can test once each spring to make sure I'm in the proper range. I really like having a saltwater pool - the reduction in maintenance is wonderful.

[waterbear]

One more thing on the salt readings from the Autopilot vs. using a test kit. I had to look it up to make sure I hadn't "mis-remembered" that the reading will be affected by water temperature:

http://en.wikipedia.org/wiki/Electri...ure_dependence

My water is about 78-80 degrees now. I don't know off-hand what temp the SWG would have been calibrated at. I'm not too concerned about that since I can test once each spring to make sure I'm in the proper range. I really like having a saltwater pool - the reduction in maintenance is wonderful.

The AutoPilot IS temperature corrected (this is why the output fluctuates in the readout with temperature, it's the temperature correction at work.)
The chromate/silver nitrate test for chloride ions is not without it's own set of problems so it is not the final word either. My rule of thumb, if the two readings are within abut 800 ppm you are certainly in the ballpark. I really don't expect more precision than that nor is it really needed.