Can't keep FC level above 0.1

[swimguy]

This is my first post. I am glad that I found this site a few weeks ago and have it bookmarked it. I wished that I had found this site when we purchased our pool in 2013.

The pool water is crystal clear and has been since it was cleaned after removing the cover about four weeks ago. This is the first year that I can't get the FC to increase. Weekly, I have been shocking the pool with 2 pounds of 73% Cal hypo and adding the algaecide.
Three weeks ago, I began taking the water for testing at the pool store. Each week the results were:
Week 1) FC 0.09 CYA 157
Week 2) FC 0.1 CYA 132
Week 3) FC 0.1 CYA 40

I thought that there was no way that the CYA level reduced that much in one week so I had it tested at a second pool store. FC 0.1 CYA 139
Yesterday, I received the TF-100 kit (no more pool store tests) and put it to use. That test had the CYA at 100 and FC at near 0.

Should I drain the pool water to reduce the CYA? If so, should I attempt to get it at 50? I can only go to the bottom of the skimmer each time since I don't have a bottom drain installed.

 

[jblizzle]

Welcome to TFP!!!

If you want to take control, you need to stop having your water tested at the pool stores (you data even shows why) and in vest in one of the Recommended Test Kits.
I should read the whole post before typing

Post up a full set of test results. Yes, you need to replace water to lower the CYA level, and then you will need to follow the ShockLevelAndMAINTAIN Process to take care of whatever is consuming your FC.

You can either rent or buy a sump pump which will be WAY faster and less water than trying to only replace 3" of water at a time. Or can you just setup a siphon with a hose?

We also do not "shock" with cal-hypo and do not recommend the use of expensive algaecides.

 

[Texas Splash]

A little draining ahead of you, but not too bad if the CYA is indeed close to 100 and not higher. Welcome to TFP!

 

[swimguy]

Week 1) FC .09
TC 0.37
pH 7.8
CH 171
TA 87
CYA 157

Week 2) FC 0.1
TC 0.2
pH 7.6
CH 161
TA 96
CYA 132

Week 3) FC 0.1
TC 0.4
pH 7.6
CH 181
TA 90
CYA 40

Using the TF-100 kit
TC 0.5
pH 7.5
CH 175
CYA 100

 

[jblizzle]

What is the FC and CC? Did you do the FAS-DPD chlorine test? TA?

I am ignoring everything before the TF100.

 

[Texas Splash]

Swimguy, what a difference in numbers with your own test kit huh? Looks like you still need to do a bit more water exchange though. Next time you post your results, please post all of them as follows:
FC
CC
CYA
pH
TA
CH (not normally necessary for a vinyl pool, but okay to post)

It will help us all. Glad you got that kit!

 

[PAGirl]

Your CYA could be above 100. You can follow the instructions for diluting (step 9 under testing CYA) to find out if it is.
Pool School - CYA

 

[cowboycasey]

Your CYA could be above 100. You can follow the instructions for diluting (step 9 under testing CYA) to find out if it is.
Pool School - CYA

+1, I agree, your CYA may be closer to 200.. post up you new numbers and we can get you going

 

[JoeSelf]

You can drain past the skimmer using a vacuum hose and vacuum head at the bottom of the pool. I had to do a 50% drain and this is how I did it.

 

[swimguy]

Thanks for the replies. Non stop rain has prevented further testing. I'll post them over the weekend.

 

[swimguy]

Yesterday, I drained the water to the bottom of the skimmer. I added three inches of water . Afterwards, it rained 1.5 inches. Just before dusk, I added 2.5 pounds of cal hypo (getting rid of what's left before switching to regular chlorine) About 30 minutes ago, I used the TF 100 kit and got the following results.

TC 4.0
CC 1.0
FC 3.0
TA 160
CYA 100 (I used the step 9 method)
pH 7.5

The water remains very clear.
Thank you for your help

 

[Texas Splash]

Those are good improvements. Now just remember to refer to the Chlorine/CYA Chart table. A CYA at 100 requires a "minimum" FC of 7, target FC of 12. And that's IF the CYA is only 100. Yours may still be higher, so you may want to increase that FC and/or continue some more partial drains while there are rains in the forecast. If you have any more questions, give us a shout.