My wife took a sample to the pool store, so take it for what it is worth.
CYA - 133 (which makes sense why my FC is low)
FC - 0
They told her to add 4-5 lbs of shock and it should take care of it. We just moved in to the house in Nov and we are learning the pool world. I believe the problem with the CYA being so high is that they have always used the 3" chlorine tabs and bags of shock that contain cya. It has added up over time. According to the pool calculator it says to drain 70% of the water out of the pool. Hoping I can do something esle instead. I used 10% liquid chlorine to get the FC level back up to 5, so we will see. When I ran my CYA test it didnt break it down to that high of a level. The first reading on my test kit was 100 and I was below that line. I would say the 133 is pretty accurate about where it would have been. Funny thing is the pool store normal levels are 30-200. After reading about CYA I realize that this is way too high. Any thoughts on what I should do next?
You need to do an extended test.
If your CYA level is 90 or higher, repeat the test adjusting the procedure as follows:
- Fill the mixing bottle to the lower mark with pool water.
- Continue filling the mixing bottle to the upper mark with tap water.
- Shake briefly to mix.
- Pour off half of the contents of the mixing bottle, so it is again filled to the lower mark.
- Continue the test normally but multiply the final result by two.
http://www.troublefreepool.com/threads/24188-Extended-Test-Kit-Directions
Your FC target is approx. 13% of your CYA, you should never let it drop below 7%. Shock level is 40% of your CYA. That 5ppm is doing nothing for your pool.
If your CYA was 140 (always round up to nearest 10) you would need to maintain a FC target of 18ppm, never going below 10ppm, with a shock level of 56ppm.
I fear your CYA is even higher.
Your FC is not low because of your CYA level. It is low because algae/bacteria/virus have taken hold of a pool without sufficient sanitizer for it's (unknown) CYA level and is oxidizing the chlorine as fast as you put it in.
Dom