Green Pool

[redhed100]

Ok, I was doing so good - this is my first year of having a pool, and then I got algae.

So I went to the pool store and the lady there sold me 3 gallons of shock and I used them according to what I have learned here and what she told me.

It is now day 4 since I started adding shock and the pool is starting to look great again, just a few poofs of green when I brush the bottom. What I am worried about is my test results.

FC = 40 (yes I have a TF-100 kit and that is what I got)
PH = 7.4
TA = 110
CYA = 85 (this was 80 four days ago, 70 two weeks ago, and I have not added it since the beginning of the season)
Pool is an above ground - vinyl liner - 8600 gallons.

We have backwashed the pump 3 times in the past 3 days. We had to add water - about 6 inches yesterday - and it rained about 3 inches last night almost making the pool overflow.

So I am concerned about the FC reading. I don't think that is even swimmable is it? It doesn't smell strong. How long before it goes down?

Also the pool store lady said that my CYA was low and it should be between 100 - 130. Everything I have read here and in my test kit says 30-80. Who is correct? She has been doing this for 20+ years, and if she is wrong, I can't imagine how many people have bought a ton of chemicals to "fix" their water based on her advice. Please help!

Thanks in advance!
Colleen

 

[chem geek]

Use The Pool Calculator to calculate dosages. Remember that with the TF-100 test kit, each drop with a 10 ml sample is 0.5 ppm so divide the number of drops by two to get FC. If your pool is exposed to direct sunlight then the chlorine should drop though with the high CYA it might drop by only 20% so maybe from 40 to 32 or thereabouts after a day. The varying CYA readings are just test error so just call it around 80 ppm.

The pool lady is wrong, especially if she says to keep your FC level low (such as 1-3 ppm). As to whether the pools of her customers have problems, that depends on the amount of algae nutrients in those pools and whether they are using any supplemental algaecides or doing weekly shocking, all of which can delay problems at least for a while.

The shock level at 80 ppm is at least 21 if not 31 (based on whether you use The Pool Calculator or the Chlorine / CYA Chart in the Pool School) -- higher chlorine levels kill and clear a pool a little faster. You should only let the FC get below the shock level when three things occur: 1) your pool is clear of algae (no visible green or cloudy dead algae), 2) your overnight FC drop is <= 1 ppm, 3) you have <= 0.5 ppm CC.

 

[redhed100]

I guess I am really lost. I am confused by the reply to my post. I now understand that correlation between CYA and chlorine, however, with my readings around 80, and I have not added it since the beginning of the season, and I have added/replaced water several times, is that a good number? She (the pool store lady) told me it should be 100-130 for CYA, where my TF-100 test kit says between 30-80. So what is correct?
What is the safe level of chlorine to swim in? Although when I tested it last night, the TC was 40, it does not smell strong in the pool. I have not added bleach since Thursday night. It has been cloudy, so maybe that is the problem? Can I swim in it? It looks stunning!!!!!!! This morning the pool is sparkling clean, there was just a bit of debris, leaves etc., that I have vacuumed up.

 

[redhed100]

Remember that with the TF-100 test kit, each drop with a 10 ml sample is 0.5 ppm so divide the number of drops by two to get FC.

This is confusing as well. I have followed the instructions on the lid of the test kit which says to multiply the number of drops x .5 and record the results as FC. Have I been doing this wrong the whole time? Although I suck at math, I know how to use a calcuator, and the answer comes out the same anyway.

 

[lightingguy]

Hey Colleen,

Dividing by 2 and multiplying by 0.5 for the FC test should result in the same number. So for a FC of 40 you would have used 80 drops of R-0871.

The pool store lady is way off recommending a CYA of 130. That's crazy talk. As you know, too much CYA makes chlorine significantly less effective. As far as coming to terms with the idea that the "professional" pool store lady and some strangers from the internet disagree.... There is a lot of really detailed science posts here and thousands of users and no one is trying to sell you anything. Like a lot of people here my local pool store sold me expensive products I didn't need, gave me bad advice and could never solve my problems.

As for your actual CYA number - to clarify - how much CYA did you add at the beginning of the season? Did you start up around 130?

 

[redhed100]

I added a container, as instructed by the pool lady and the guy who installed it. My testing has shown levels of 70-80 all summer. I have not added any since the beginning. I know the test can be subjective.

So no matter what, what are safe levels of chlorine to swim in?

BTW - I do trust people on here more than the lady at the store, I just can't believe that you can get such different answers about pool water, which is chemistry, a science. I guess it is just really frustrating, because when she said that, I was thinking, does she really know better and is telling me a load of Crud on purpose? I know they want to sell you stuff, but to lie in your face? Or is she just that stupid?

 

[frustratedpoolmom]

I think they just repeat what they have been told by industry reps who don't know or want to know any better.

It is safe to swim UP TO shock level - based on your CYA.