Pool Still has Chlorine? Worried about CYA.

Mike in Vermont

New member
May 14, 2019
3
Vermont
This is my second season opening my pool (I bought the house in July of 2017). Late last season, after using too many tri-chlor tablets I had some chlorine lock problems and some very high CYA levels. I attempted to recover with a partial drain and refill with limited success but it was late in the season to be using an unheated pool in Vermont so I lowered the water level by about 2 feet and closed the pool for the season.

We had enough rain and snow since the fall that the pool level is right back where it should be and I decided to start the opening process last weekend while the water was still pretty cold (high 40’s) and before it had a chance to develop much algae.

The first thing I did was grab my Taylor K-2006 Test Kit and ran some tests…
PH = 7.2
TA = 100
CC = 3.2
CYA = 45

My first question is about the chlorine level. Without having added chlorine since last September I was surprised to find chlorine in the pool. Is this normal? Did I have enough CYA to stabilize the chlorine for the past 8 months? Granted, I did add massive amounts of chlorine last August and September when I was struggling with chlorine lock.

My second question is about my CYA level, which after my chlorine lock problems I am very sensitive about. When I did the CYA test I took my reading after I couldn’t see the black dot with a fair amount of effort (ie, if I could see it with a bit of effort I kept adding more of the mixed solution to the comparator tube). Is this the correct approach? I don’t want to under estimate my CYA level.

FWIW – I added three pounds of Cal Hypo and ran the pump/filter for 24 hours and saw significant improvement in water clarity. When I first uncovered it I could see the bottom drain but not the pattern of the liner, after 24 hours I could see the liner patterns so apparently three pounds of Cal Hypo was enough to make a difference which would tend to suggest that my CYA level is ok, right?

I’m tempted to bring a water sample to the local pool store to be tested with the ALEX system so that I have something to validate my testing against but I’ve heard mixed things about the reliability of ALEX.

TIA!
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Welcome to TFP! :wave: Since you mentioned having chlorine, I'm assuming the item above listed as 3.2 is actually free chlorine (FC) and not CC?

Sounds like you have some residual algae issues from opening. If that's the case, you should follow our SLAM Process page. To do that however, you need to test the water on your own consistently and as much as needed to maintain the proper SLAM FC level noted on the FC/CYA Chart. As such, I would round-up the CYA to 50 and increase the FC to 20 and SLAM Process. Use regular bleach to increase and maintain the FC level. Works much better without any side effects.
 

Mike in Vermont

New member
May 14, 2019
3
Vermont
Yes, I intend to SLAM (with bleach) in the next couple of weeks but I want to be sure I have the basic chemistry and especially the CYA dialed-in first. If I’ve under-counted my CYA level and I need to go thru another round of draining and refilling I’d like to do that before I SLAM. Last season the solar cover was enough to keep the water temp above 80 for most of the summer and I’d rather not drain and refill after the pool water has had a chance to warm up.

I suspect my CYA level is ok, but my chlorine lock problems last season have left me a little hesitant to charge ahead until I’m sure.

At this point I have a bit of cloudiness and some algae, but not much and with temps in the 40’s today and snow at higher elevations last night it’ll be a few weeks before even my hot-blooded 10 year old is ready to go for a swim.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
I suspect my CYA level is ok, but my chlorine lock problems last season have left me a little hesitant to charge ahead until I’m sure.
Mike, when you get a moment, I would encourage you to do a quick search on our forum for chlorine lock. You'll see what I mean. :)

Once you get ready to pull the trigger on that SLAM, just let us know. Sooner the better if that water is still chilly. :)