Trouble Keeping Chlorine Levels Up

[AlexLaz]

I'm new to this site and also a first time pool owner. After having a really frustrating experience with the local pool stores, I came across this site and decided to take the matters into my own hands. After opening up my pool for the first time this season, the water was cloudy with some visible algae. The CYA level was at 120. I drained 50% of the water and re-filled it from tap.

I have a 20,000 gallon vinyl Non-SWCG in-ground pool. I also purchased the TF-100 test kit.

After the initial re-fill and the SLAM process I got my numbers to:
FC = 4.5
PH = 7.8
TA = 130
CH = 200
CYA = 40

I was able to maintain it for about a week at the appropriate levels, but now that the temperatures are starting to climb up (in the 90s), it seems like I'm losing most of the chlorine over night. I've been trying to bring the FC level to at least a 5. I add 10% liquid chlorine from Walmart based on the pool math calculator numbers, but when I check the levels, the FC hardly makes it to 1.5. I'm also seeing a slight drop in other numbers:

This morning test results:
FC = 1
PH= 7.5
TA = 90
CH = 150
CYA 40

The pool looks great with no signs of algae, so far... What could be causing the chlorine to drop? I'll greatly appreciate any suggestions on how to move forward!

Thanks in advance.

 

[AftonJeeper]

Sever factors could be causing it. The size of your pool may be off which would explain why you can't get to the FC number your shooting for. Algae could be starting causing the increased demand for chlorine. Chlorine could be old and ineffective, check the date code. IIRC the first 2 numbers are the year and the next set of numbers are the day it left the factory. 17 170 would be today.

 

[pookiesunshine]

.... Chlorine could be old and ineffective, check the date code. IIRC the first 2 numbers are the year and the next set of numbers are the day it left the factory. 17 170 would be today.

somebody else reported they got some old chlorine. when you pour it into the pool, does it smell strong? look pale yellow? yes i know this is subjective....

 

[Razorhog]

You might try getting a few jugs of regular great value bleach and see if your FC responds differently. After adding wait 20-30 minutes for it to circulate and test to see if you hit your target. If not, I would suspect algae.

 

[AlexLaz]

Sever factors could be causing it. The size of your pool may be off which would explain why you can't get to the FC number your shooting for. Algae could be starting causing the increased demand for chlorine. Chlorine could be old and ineffective, check the date code. IIRC the first 2 numbers are the year and the next set of numbers are the day it left the factory. 17 170 would be today.

Thanks for the pointers! I never did calculate the size and only relied on the number given by the pool store that they had on record, I assume from the previous owner. Will check the dates too.

 

[AlexLaz]

somebody else reported they got some old chlorine. when you pour it into the pool, does it smell strong? look pale yellow? yes i know this is subjective....

Thanks for your reply! It doesn't have strong smell at all, but looks a bit yellowish.. I'm storing it in the garage that does get pretty hot during the day.. now I'm thinking that could be the reason..

 

[AlexLaz]

You might try getting a few jugs of regular great value bleach and see if your FC responds differently. After adding wait 20-30 minutes for it to circulate and test to see if you hit your target. If not, I would suspect algae.

Thanks, yes will give it a shot.