This is another of my "I'm just curious" questions, so most of you can simply shake your heads and move on.
This quote is from another thread:
First, let me say that I would normally get the water sample from much deeper in the pool, and not while the pump had been off for any length of time, but...Originally Posted by JasonLion
Last week, after the pool finally thawed, I pulled out some water to test. Since the pool was still covered, and the water level was still down, I took my sample from only about 3" below the surface by sticking my hand through the skimmer. (I did this mostly because I was bored and wanted to play with my chemistry set. ) When the pool is open, I get my samples from about 18" deep, but I couldn't reach that far this time. Keep in mind, that this is under a solid black winter cover, so there shouldn't be much UV getting to the surface of the water.
At that time, my FC had dropped to 0.5, CC was <0.5 but was >0.0, and my CYA was down to 40. When I closed last fall, my FC was 6 and my CYA was 70. Since my FC was so low, and I didn't want to deal with an algae bloom later, I went ahead and filled the pool up again and got the pump running.
After running the pump for about 6 hours, I tested again, again getting the sample the same way. This time, the FC = 2, CC = 0, and CYA = 50. Since I added 8" of water, that is a 20% addition, which should have diluted the chemicals by 20% as well, correct? So, my CYA should have been down to 32, and FC below the bottom end of the scale.
OK. I added about 8" of water, so this means I replaced about 17% from my fall level. CYA 70 - 17% = 58, FC would slowly drop anyway, even with the pool covered, so we won't worry about it.
Finally, after all that, here are my questions:
Since the water sat dormant for 5 months could the CYA and chlorine drop partially (but not fully) out of suspension so that the top layer had lower levels than the rest?
My water froze to at least 3" over the winter. When the water freezes, do the chlorine and CYA drop out of suspension? This would easily explain why the top few inches had lower levels before the water was stirred up again, and the numbers climbed back up after the pump was running. If that was the case though, I'd expect the numbers to be even lower, since the sample came from the top layer.