Help! My pool will not hold chlorine

Jake0497

Member
May 26, 2012
5
This is pretty long winded but here it goes. Our pool seems to be in a "chlorine lock". Over the last 2 weeks we have added close to 60 pounds of shock and FC and TC are still at 0.5 we were told that something was eating up the chlorine and they tested for the dreaded phosphates which came up at 3000! We treated with phos free and 48 hours later we back washed our pool and cleaned the de filter then added 5 pounds of shock. For the first time in 2 summers we held the chlorine but only for about 36 hours then it was back down to 0! We shocked again and it held again for only a few hours. Phosphates were retested and they are at below 100. What now??????

TC .3
FC .2
Ph 7.5
alk 160
CH 200
CYA 40
 

zea3

Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
11,720
Houston, Texas
Hi, welcome to TFP! We will be happy to help you figure out what is going on, but I have a few questions first. What size is your pool? In ground or above ground? Plaster, vinyl, or fiberglass finish? Do you know what is the active ingredient in the shock product? What are you using to test the water?
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,880
Silver Spring, MD
Welcome to TFP!

Phosphates are not the issue here. I suggest you do some reading in Pool School, see the link in my signature or near the top right on any page, especially the section on how to shock your pool. The answers to zea3's questions will help us figure out what the best next step is.
 

Jake0497

Member
May 26, 2012
5
We have a 34000 gallon vinyl line pool with DE filter. I have been using accuchek 7 strips and also taking the water to the pool stores for testing. We have tried several types of shock including Dichlor and calcium hypo.
 

JasonLion

TFP Expert
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LifeTime Supporter
May 7, 2007
37,880
Silver Spring, MD
The dichlor will have raised your CYA level, requiring higher FC levels to kill algae. Test strips are only so so at best. They can be especially far off on CYA readings.

The key to killing algae is to have reliable test results and to be diligent about maintaining the correct FC level, especially on the first day.

If CYA is around 50 (guessing, assuming higher due to dichlor usage), you need to keep FC at about 20 consistently to kill algae. That may require adding chlorine as often as hourly for the first day. For more details on shocking your pool, see the article in Pool School.
 

duraleigh

Admin
Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
32,852
Sebring, Florida
You should keep your FC at shock level until you meet the following criteria...

1. Your pool water is sparkling
2. Your CC's are .5ppm or less
3. You can hold your FC overnight without losing more than 1ppm.
 

Jake0497

Member
May 26, 2012
5
Ok.. So we have done everything as instructed about keeping the FC at a level of 20 and we have succeeded! The FC has been at 20 for 48 hours... Now what?? How long do we let the chlorine level stay so high? Will it come down?