First water test results

[Daggit]

No, not from the vaunted but still unseen test kit, but from the PB who re-plastered.

TDS 223
CYA 39
Alk 100
Ca 212
pH 7.5
Cl 1.0
Co 0
NaCl 0

this all looks Ok to me, from what I've read here. I just stopped him from putting the new skimmer baskets in with, I think, half a dozen pucks in them. This pool gets very little direct sunlight what with all of the tree cover (large live oak right behind diving board) so I should be alright with moderate CYA levels.

What is a good target for calcium? Any other thoughts.

[chem geek]

The numbers look good except for the Free Chlorine (FC) level which is too low at the 1 that you show. See Ben's Best Guess CYA chart that says you should have a minimum of 3 ppm at your CYA level. You could even live with a lower CYA level than that if you wanted to maintain a lower FC level. With mostly shade, a CYA level of 30 should be plenty and even 20 will give you a good amount of protection (i.e. longer chlorine life). You can look at this chart to see that 20 ppm CYA at 5 ppm FC gives a half-life of around 5 hours and that's in direct noontime sunlight which you don't have. Your CYA may drop over the winter as some people notice this phenomenon.

So yes, you were right to stop him from putting TriChlor pucks into your pool, but you can add some liquid chlorine (bleach) to increase the FC a bit to 3 ppm or so.

The TDS number (223) is impossible given the TA and CH that you have. Just these two items alone, which are essentially from Calcium Chloride and Sodium Bicarbonate, would give you a little over 400 ppm TDS (the calculated amount, including the CYA that you have, would be about 430 ppm TDS). Even if all of the calcium came from the curing plaster and not from calcium chloride, you would still have more than the measured TDS number. However, don't worry about the TDS number. It isn't important in water chemistry until it gets really huge and even then is of somewhat minor importance compared to other factors such as pH.

The CH you have (212) is OK. A more normal ideal number would be in the range of 250-300, but this isn't a big deal. The change in water balance between 212 and 300 is 0.12 and we only start to even think about water balance issues when we are at 0.3 and even then only start to see issues at 0.7 or even 1.0 so you are a long way from any problems. Also, since this is a replaster job, it is very likely that some plaster dust or calcium hydroxide from curing will get into your pool water over time and raise the CH automatically -- I'll bet the PB knew this and set up your initial water balance on the low side. After a few months, the CH should level off close to its "final" value, though some people have noticed CH and pH changes up to a year. The other thing you may notice is for the pH to have a tendency to rise as part of the curing process of plaster (which produces calcium hydroxide).

You should get your own test kit and if you are still waiting for Ben's, you might consider cancelling that order and getting one quickly from Taylor -- the K-2006 test kit -- or from some other source.

Richard

[Daggit]

Damn, you're thorough. I actually did add a half-gallon of bleach last night since I knew it had to come up but had forgotten what bleachcalc had told me I needed for each ppm of increase (0.4 gallon as it turns out) and didn't want to do the dilution calcs by hand.

Regarding the test kit, I confirmed yesterday that the local pool store has the Taylor kit in stock, so I cancelled the order with Ben this morning and will have one in my hands today.

Thanks again.