noobie's numbers

[Donna's Poolboy]

First off, this forum has been an amazing source of information! Thanks to you all. I wound up here out of frustration at not understanding all these crazy numbers.
I've been soaking up all the info posted here, and I've got some numbers.
We have a 23,000 IG with a vinyl liner. I'm using an HCH drop test kit (until Ben's kit arrives ) and here's what it tests at:

FC- only reads up to 5.0, but the dark yellow tells me it's probably close to 7
ph- 7.2
ALK- 170
CYA- 90
CAL- 0 actually, no reading...5 drops of indicator and the sample wouldn't trun red.

Here are today's numbers from the pool store:

TC: 5.1
FC: 5.1
CC: 0
ph: 7.5
ALK: 111
adjusted ALK: 71
CYA: 134
Hardness: 256

The water is 84* and crystal clear. Rather than just turn the numbers over to you guys, here's my noobie analysis. Let's see if I've learned anything:

1) There are flaws in both sets of numbers (the HCH test can't give me accurate CL numbers beyond 5 ppm and I KNOW the water has at least some calcium in it because I used calcium based shock last season and this season.) With a vinyl liner in our pool, I'm not too worried about it.

2) I question the CYA reading from the store. He uses a visual test just like the HCH test so I don't know how he can get a number like "134". 120 or 130 maybe. Also, yesterday when they tested my water, the CYA reading according to the print out was 65. I refuse to believe I had a 69 point jump overnight ! I'm gonna rely on MY test which appears to be 90. (high, but livable)

3) ALK is fine no matter which numbers I use. Again--vinyl liner. ph seems to be stable. I'm leaving it alone.

4) Their test shows the FC and TC both at 5.1, thus no combined chlorine. Theirs is above 5; mine is above 5. If my CYA reading of 90 is accurate (and according to my noobie eye, it is) using the best guess chart, my free CL needs to be at least 5 ppm so I should be in good shape.

After looking at the numbers, I've done nothing to the water today. I'll test the chlorine after the kids get done fighting--err, swimming and try to keep it just above 5 ppm.

Now I'd like to hear your evaluation.
(I feel like a college kid who just submitted his term paper!) Gotta run...my wife needs more ice and lemonade on the pool deck!

Thanks in advance,
Bill

[aylad]

Bill,
good job, get yourself a glass while you're at it!!!

Your analysis is very good, as far as I'm concerned. Regarding the Ca, in the vinyl pool, it doesn't matter, as long as it doesn't get too high. If you're below 400 and don't use Cal-hypo for chlorination or shocking, that's fine. Ignore it.

Your alk is fine, as long as your pH is stable. If your pH starts to bounce, you can raise it a little with Arm & Hammer, but if it's stable, leave it alone.

You're right in that CYA of 90 (and that's the number I'd go with, too--I ALWAYS trust my drop-based numbers over a pool store's!) is a little high, but liveable, just keep your base Cl at 5+ and you're good to go. However, I'd stop using the CYA source (trichlor pucks? dichlor shock?) and stick with bleach.

Just a note to ballpark Cl over 5--use CarlD's shotglass method--use a shotglass of pool water, a shotglass of distilled water, mix thoroughly, then take your Cl test sample from that. Read your results, multiply by 2. Looses a liittle accuracy in the dilution, but will get you close enough.

Happy swimming!!

Janet