New guy question about rapid drop in cya level?

[TampaPoolNerd]

First off folks I really appreciate the wealth of information and efforts provided by the admins and members of this site. I've been in my first pool home for right a year now and have used this site numerous times to not only learn about all my equipment but how to efficiently and economically plan and use such equipment. This plus learning about the chemistry has enabled me to get our pool efficiently dialed in. So thanks all!

Quick question about cya. Would search the forums but I'm heading to La in a few hours and need to get packing. To keep it simple I use the k2006 test kit and all levels are dialed in exactly per my "goal" levels on the pool math calculator.

FC: 5.5 ( high bather load; no CC; and cya steady around 38 for the past two weeks)
CC: 0
Ph: 7.6
TA: 100
Ch: 250
Cya: again steady for a few weeks (tested the last two days 38 &37). Then today it's reading low off the scale. Ie. I filled the whole test tube up and could still see the black dot a little.

Therein lies my question?? Using one Trichlor tab to assist liquid chlorine which should maintain if not slightly raise cya correct? Why such a dramatic drop in 24 hours. We've had a few light rain showers in this time period but not much. Lots of Uv in a screened in pool cage so I want to make sure those cya levels are back up to protect my FC. Thoughts??

Thanks again folks!!

 

[ThinkPad]

Welcome to TFP!

Using one trichlor tablet will raise the CYA by about 2.4 ppm. You can use Pool Math to see how much of one chemical will affect your levels (at bottom of page).

There is another topic here about CYA degration. You should read it. I don't know much about it.

 

[Pflugerpool]

Just so we understand that you're performing the CYA test correctly, how are you getting values of 37 and 38? The Taylor CYA test is graduated in 10 ppm increments, and accuracy is generally considered to be ± 10. In other words, you shouldn't be able to discern a 37 or 38 using your kit if you're doing the test right...

 

[TampaPoolNerd]

Yea I've been using the pool math page. Sorry I understand the effects of adding the tabs and cya. What I don't get is the reduction of cya so dramatically in a 24 hour period even while using a tab. Haven't seen this happen before.

As far as the test goes. I'm speaking in assumptions between the 10 ppm values. Sorry for not being more specific. Upper end of 30-40 is around 38 in my notes. I've seen such small fluctuations that I've narrowed it down to small increments. .
Even so to see a drop of close to 40 to what appears to be below 30 is a pretty big drop correct?

 

[jblizzle]

Was the lighting the same for all the CYA test? Was the water in the pool well mixed after the rain or was rain water still on the top of your pool?

 

[TampaPoolNerd]

Same time of day for the last three days. Bright outside bu test completed under porch awning. Pump running during rain showers yesterday and again today. Should be equally mixed I believe.

 

[TampaPoolNerd]

Thinking back all I can think of is that I didn't reach far enough (18" or so) into the water to collect sample. Which I normally do OR there indeed was some residual rain water left in the upper 1/3 of my pool water. Either way I took two separate tests and yielded the same results. Unfortunately I now have to wait a few days to do follow up testing. ( or explain to my mother in law how to do it, Ha!) Either way it's great to be here and having fun learning both the chemistry behind my pool. Also enjoying learning the equipment/chemistry setup required for my new (used and obtained for free.99) dual-tap beer kegerator for our back pool patio. It's going to be a great summer time and fall football season this year.

 

[Vince-1961]

dual tap beer kegerator?

 

[TampaPoolNerd]

single tower, dual faucet, dual tap/pressure regulators/hoses for two different types of brew.

 

[jmbradwell]

Don't care what kind of brew as long as it's cold and I'm not paying for it.