Chemical Balancing Questions

Master Shake

Member
Apr 30, 2009
10
Hello,

I opened my 5500 gal Intex metal frame / vinyl liner pool yesterday and noticed it was somewhat green and a little slimy on the inside walls. I added two 13.5oz packs of Kem-Tek tri-chlor 67% (60.3% available chlorine) shock and one 1.0 gal 10% chlorine, and ran the filter all day. I also brushed down the sides to loosen up and remove the algae (or whatever it was) and could see it suspended in the water. The water was also too cloudy to see the bottom (~50 inches). At the end of the day, my chlorine reading was only 2.

This morning, I brushed down the inside again and vacuumed the middle. The water is less green, but still very cloudy -- still can't see the bottom. I added another 13.5 oz pack of Kem-Tek shock and another one gallon of 10% chlorine. I ran the filter all day again and at the end of the day the chlorine reading was 3. According to the package, these 13.5 oz packs of shock are supposed to be rated at 2.25 oz added to 10k gal = +1.0 ppm chlorine.

A few hours later, I ran a full test (TFT-1000 kit). My numbers are:

ph 7.6
FC 2.5
CC 3.5
TA 120
CY <20
CA N/A (Intex pool)

My questions are: Does the CC reading mean that the chlorine is killing off the algae and/or whatever else organic is in the pool? Will it be caught and removed by the sand filter eventually? Do I need to run any kind of clarifier or flock? Or just keep the chlorine high?

Last year, I had a CYA reading of over 100. I've always heard that it never disappears so I usually avoid the tri-chlor tablets and shock. Why is the CYA reading now less than 20? I've never drained the pool -- just add a few inches of water per week due to evaporation. Does algae or something else dissolve CYA? Does this mean I can stick a bunch of tri-chlor tablets in until I get the CYA back up?

Finally, am I losing so much chlorine because of having no CYA? For 5500 gallons, and what I've added over the last two days, I was expecting my chlorine reading to be 20 or more. I live in Arizona, and it was 100 and sunny today. I get about 6-7 hours of direct sunshine, but I usually only lose 1 point per day of chlorine due to the sun. I am thinking the loss is because of very low or no CYA, and the algae? But for such a small pool, I am not sure if I should be adding so much chlorine.
 

JohnT

Admin
Mod Squad
TFP Expert
Apr 4, 2007
9,475
SW Indiana
Master Shake said:
My questions are: Does the CC reading mean that the chlorine is killing off the algae and/or whatever else organic is in the pool?
No, it means it's trying to but there isn't enough chlorine to do the job. When you raise it to shock level, keep it there. That may mean adding more chlorine hourly at first.

Master Shake said:
Last year, I had a CYA reading of over 100. I've always heard that it never disappears so I usually avoid the tri-chlor tablets and shock. Why is the CYA reading now less than 20? I've never drained the pool -- just add a few inches of water per week due to evaporation. Does algae or something else dissolve CYA? Does this mean I can stick a bunch of tri-chlor tablets in until I get the CYA back up?
CYA often disappears over the winter in unmaintained pools. You can use trichlor or dichlor for chlorination until it gets back where it should be. Just watch it, as they add it more quickly than you'd imagine.

Master Shake said:
Finally, am I losing so much chlorine because of having no CYA? For 5500 gallons, and what I've added over the last two days, I was expecting my chlorine reading to be 20 or more. I live in Arizona, and it was 100 and sunny today. I get about 6-7 hours of direct sunshine, but I usually only lose 1 point per day of chlorine due to the sun. I am thinking the loss is because of very low or no CYA, and the algae? But for such a small pool, I am not sure if I should be adding so much chlorine.
You will lose most of your chlorine in a day if you have low CYA or if you have algae. Have both and you will go through it very quickly.
 

Bama Rambler

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2009
23,047
SouthWest Alabama
The high CC's mean that you need to continue holding shock level until you meet the criteria for being finished shocking.
The first thing you need to do is read the Pool School article on how to shock your pool. Shock is a process not a product.
Using trichlor shock ins't a bad thing right now because you need some CYA in there because the sun will burn off the FC fast without any. Just use the Pool Calc to figure out how much you can use because you don't want to go above 30ppm while you're shocking.
 

Master Shake

Member
Apr 30, 2009
10
Thanks for the replies and the help. I went out and got another 10 packs of the 13.5oz Kem-Tek tri-chlor 67% (60.3% available chlorine) shock. I added three packs just before sunset, ran the pump for 3 hours, and tested the water again. I still can't get the FC up past 6.0. According to Pool School and the chart, I need to get it up over 10 (<20 CYA).

This time, it looks like the FC is 5.5 and the CC is 15 or more (30+ drops of R0871). Does this sound right? I have never had CC this high, so I am not sure if I am doing this part correctly. The water does seem to be clearing up somewhat and is now just cloudy (not green), so maybe the water was just in a really bad situation? Also, do you get rid of CC's by just running the pool filter 24 hours a day?

I haven't tested the CYA again, since I've read it can take up to a week to fully dissolve, but with all of these tri-chlor packs, it should be building up some by now. I also have three of the 3" tri-chlor pucks in a floater as well now. Once I get the numbers under control, I will go back to just bleach.

For confirmation sake, this is what I did: According to the instructions of the TFP-100 kit, it says to add 1 scoop of the R-0870 powder to 10ml of pool water, so that the solution turns pink. Then use R0871 1 drop at a time until the water is clear (swirling after each drop). This was 11 drops, so I wrote 5.5 down as FC. I then added 5 drops of R003. This turned the water a dark, blood red! It took about 30 drops of R0871 to get it clear again, so I wrote down 15 for CC (I lost count after 25 drops or so - swirling after each drop, but it was about 30 drops total this time). Am I doing something wrong here? This is only a small 5500 gallon pool! :)
 

cheddar85

Well-known member
Feb 18, 2010
271
Houston, TX
Sounds like you're doing the test right. CC's at 15? Wow. :shock: Just keep hitting it with chlorine, and since you're using Trichlor, keep an eye on that CYA! With how much chlorine it could take to clear it, you may end up overshooting your target level, so just keep an eye on it and switch to bleach when you get there.

Keep at it, and post any more questions you have! Everyone here is glad to help!
 

frustratedpoolmom

TFP Expert
LifeTime Supporter
In The Industry
May 20, 2007
12,177
SWSuburban Chicago, IL
Based on the description, it sounds like your CYA was possibly converted into ammonia.... either way the process is the same, just keep shocking until the FC holds overnight at the CC is .5 or less.

However, I think you should stop using the trichlor powder. If I'm calculating correctly, you have already added enough trichlor powder that your CYA would have risen to above 50 by now.

So I'd suggest you switch to bleach or liquid chlorine to complete the shock process and check your CYA level in a couple of days.
 

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