puzzled...

[valpo]

About 10 days ago, after some serious rains, I noticed a rapid drop in FC along with some very pale yellow growth around the skimmer (slimy too). I proceeded to follow the shock process (first time I have needed to do this). Got up to shock level and continued for several days until I saw no visible overnight loss in FC and the pool water looked really good. Later that day, I did another reading and the FC level had dropped from 12 to 7. I figured that I had not been successful, so I added enough bleach to get me back to 12 that evening. This morning's read was 12. All good, water looks great. This afternoon, the reading has again dropped to 7. I am puzzled! Any thoughts?

Pool readings as of now:

FC - 7
CC- 0
TA - 80
CYA - 30
CH - 230
PH - 7.2 (this reading taken before I started the shock process.

Thanks in advance for your thoughts.

 

[pwrstrk]

Does the pool get a lot of sun ? At high FC levels with a lot of sun you can lose 5ppm.


Sent from my iPhone using Tapatalk.

 

[duraleigh]

+1 what pwrstrk said.

 

[jblizzle]

Sounds pretty normal. At a CYA of 30ppm with sun, you will likely lose ~50+% of your FC each day ... this ends up being more ppm when you start at higher levels.

 

[linen]

As others have said, since you did not lose any FC overnight then the loss during the day is likely from the sun and you can be done shocking.

At 30 ppm cya, it is not unusual to lose 50% (or more) FC if the pool gets a lot of sun. Assuming your cc <0.5 and there are no visible signs of algae, I would let your FC drop back down to normal levels and see if you FC loss is also back to normal. In the future, if your FC lose is more than 50% during the day, you could consider upping your cya level to 50 ppm which may reduce your daily FC loss to the sun to more like 30-40%.

 

[valpo]

The pool gets about 50% sun for most of the day and the last two days have been sunny. The CYA occurred to me, but I thought the loss was too substantial - I will let the FC go down to normal rates and see what happens. Will also consider raising the CYA slightly to minimize this. Thanks for the help - will let you know if things go south again!

 

[duraleigh]

Living in KC, I would suggest a CYA of 40-50 ppm....that'll cut your FC loss noticably.

 

[jblizzle]

I am seeing 60+% loss each day with a CYA of 50ppm ... but I get a LOT of AZ sun basically all day. Working on raising my CYA up even higher.

 

[valpo]

Kansas City hasn't seen much sun yet this year, but it's coming - I'll make that adjustment in my calculations this year and go from there. I have a pool that has seen better days cosmetically (was built in mid-80's), but it holds water! And on my good days, it holds beautiful water! Thanks for the advice.