Where is my CYA going?!

[TroubleFreePat]

OK, so - new pool. Trying to get CYA up. For anyone following my other threads, I've finally acurately determined my pool is about 8500 gallons.

Since we've put the pool in and have started trying to bring CYA up, we've received about 7" of rain. Not normal for our area!

Anyway, I've now added 6.5 lbs of CYA. I've probably drained about 7" of rain from the pool (Over the past month.)

Here's my numbers and a little "drain" info -

6/9/2013: Added 2 lbs of CYA (None in the water as it's brand new)
6/10/2013: Had to remove probably 2" of water from the pool due to a storm
6/20/2013: Tested CYA using ColorQ - 18. Added 1 more pound.
6/25/2013: Tested CYA using ColorQ - 30.
6/29/2013: Added 1 more pound.
7/3/2013: Drained about 2" of water from pool for another storm.
7/4/2013: Tested CYA using ColorQ - 36.
7/5/2013: Took sample to Leslie's for kicks - they show CYA at 40. Guy really seemed to know what he was doing (30 years with his own pool) and was using a Taylor kit.
7/6/2013: Took sample to local pool store for kicks - they show CYA at 53. Used something connected to their computer and it was all electronic/digital.
7/7/2013: Added 2.5 pounds of CYA
7/13/2013: Tested CYA using Taylor kit - 55. Removed 2" of water again from the storms.

Pool is approximately 30' x 14' (But it's not rectangular, so these numbers are slightly high.) But based on those numbers, I calculated that 2" of water drained from the pool should be about 523 gallons, if my math is right. So I AM replacing probably 15% of my water, basically, every time we get a big storm and I have to drain 2" of rain water.

Sooooo. . . Think the 2" of rain water is diluting CYA that much? I need to test everything else again when I get a minute and see how the rest of my numbers are. I was borderline on CH before the storm; TA was perfect before though. So they're probably both low now.

 

[pwrstrk]

I think the rain and draining has got the CYA out of whack.

I'm not familiar with the ColorQ test kit and I don't trust the pool store. I do trust the kits we reccomend.


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[DKT113]

I am on the other side of PA ~ just North of Pittsburgh & we had the rains as well.

My initial dose took me to 30, last Sunday I had to add 4 pounds, was going through bleach like crazy ~ we had a boatload of rain ~ but we had serious sun in between the tsunamis. I am shooting for 35-50 ~ such a wide range because I really didn't have optimal conditions to test before redosing, but I know by the bleach I was going through in these conditions I didn't hang onto much of the initial 30.

Just was a funky wet opening season. You can kind of gauge when you have a sunny day if you are below what is recommended. Undershoot it just because it's very easy to add more if you need it, but when it gets away from you and you have too much it's a hassle to maintain the chlorine demand and get the CYA to a manageable level.

Remember it does take a week for granular to register. During that week I just dose as if it's in there even though I haven't officially seen it with my testing.

 

[JasonLion]

Even under ideal conditions the ColorQ doesn't have the precision that you want to measure CYA levels. Still, several other tests show levels only somewhat higher than the ColorQ, so that does not appear to be the primary issue here.

6.5 lbs of CYA in 8,500 gallons should have raised the CYA level to around 100. Draining water would have lowered that by something but not nearly that much.

Is it possible that your pool holds more water than you think it does? A 30'x14' oval 3' deep would be around 8500 gallons. But if the water depth is any deeper than that, it would hold more water and that would fit with your test results better.

By the by replacing 2" of water is a 3' deep pool would cause a 5.5% reduction in CYA. Replacing a total of 7" would be only 20%, and that much only if done all at once. Done is several steps, as you did, would have lowered CYA by less than 20%.

Another possibility, though not especially likely, is that what you have been adding is closer to 50% CYA rather than full strength. It is quite rare, but occasionally an off brand is only 50% concentration.

 

[TroubleFreePat]

Well, I'm now on to the Taylor kit and got rid of the ColorQ, so, that variable is gone.

I'm now 99.9% confident in having 8500 gallons in the pool. When the pool was installed, the water truck dumped 5500 gallons. I added another 3000 as per my water meter. I spoke with a guy at Leisure Pools who was responsible for filling and draining their pools to determine capacity, and he said I was right on with 8500.

The pool has lots of curves and LOTS of steps that should be displacing a fair amount of water. Below is a shot of the pool as it was going in. Depth of the pool goes from 3'8" to 5'7".

I thought about the CYA not being 100% as well; unfortunately the bag doesn't show a percentage anywhere. . . And you are correct, I also thought about the fact that the various storms were dilluting the water over time - since we didn't drain 6-8" at one shot, I didn't know a good way to math this out.

Anyway, sounds like I'm on the right track and not missing something obvious. I'm going to throw another pound in tomorrow to get me up to (What should be) 70. We'll see how that goes as the week doesn't look terribly rain at this point.