Cannot raise FC level above .5 to .8

[FixRFill]

I have opened the pool and the water looks great. However, I cannot get a FC above .5. Twice in the last couple of weeks I have added more than 12 cups of dichlor (each time) and have had little change in the FC level. Last night I added 9 large jugs of bleach (about 13 gals) and 15 minutes later the FC reading was unchanged at .5 to .8. I poured a qt of bleach into the swimout part of my pool (dead spot) that is perhaps 3 1/2 ft x 1 1/2 ft and perhaps a foot deep. I took a reading a minute or two later and the FC level was still unchanged. I'm using a Taylor K-2006 with the following latest results.

FC: .5 to .8
CC: 2.0
Ph: 7.0 (in process of attempting to raise)
TA: 85
Hardness: 230
CYA: 25-50 (Hard to measure.)

 

[jblizzle]

How old is the testing kit? Where has it been stored? Just wondering if some of the reagents have gone bad as it seems odd you would get so little change.

You may need to wait longer than 15 minutes with the pump running before you retest.

 

[chem geek]

Welcome to TFP!

Did your CYA drop over the winter and was the pool "let go" so that it had zero chlorine? If so, then it's possible that bacteria have converted some CYA into ammonia. If you add chlorine and then measure 5 minutes later, do you get a Combined Chlorine (CC) reading even if the Free Chlorine (FC) is 0? If so, then you likely have ammonia in the pool and can do a bucket test using pool water to see how much chlorine it will take to clear. 1/4 teaspoon of 6% bleach in 2 gallons is 10 ppm FC.

 

[Poolschoolgrad]

You added 13 gallons of 6% bleach to a clean 23k gal pool and the free chlorine only increased from .5 to .8 ??
This should have raised the FC by 35 ppm.

Maybe there is an error in how you performed the test.
Please tell us about your testing procedure using the K-2006.
List the regents used and the sample size.

PSG

 

[frustratedpoolmom]

If you do have ammonia in the pool the FC won't register - it's consumed almost instantly, and the CC is high, as is the case with yours. The solution is more chlorine - but if you want to confirm ammonia you can purchase an ammonia test kit from a pet supply store (its for fish tanks).

 

[FixRFill]

Thanks for all the responses. The pool kit is brand new. Also, I have beem testing with an OTO kit to make sure my K-2006 reagents were not bad and the OTO results match (light yellow then turning darker to show CC around 2-3) the K-2006. I am using R-0870 powder (2 dippers), R-0871 and R-0003. I have run many test using both the 25ml sample (multiplying by .2/drop) and the 10ml sample (multiplying by .5/drop). Also, I have run experiments my adding chlorine to tap water and it appears to test fine.
I'm not sure how much the CYA dropped over the winter. I topped the pool off with about 5K gallons when I opened it and the pool store measured CYA at 22 (before I added all the dichlor/trichlor).

I have a lot of problems with pink algae (bacteria) every year and have been unable to control it. I did close it last fall with some evidence of pink algae and it was there when I opened the pool (always is). The shocking cleared up the pink algae but now I have the FC problem. I have found in the past (15+ years) that the sure cure is to drain and refill the pool but I am determined to figure this thing out this year.

I should mention that I have also used MPS to shock the pool so it may be giving me a false CC reading. I have ordered the Deox reagent to neutralize the MPS but have not received it.

It sounds like ammonia may be the culprit. I will buy more bleach and try the bucket test and perhaps buy an ammonia test kit.

 

[FixRFill]

It has been a strange but eventful day around the pool.
First, I got my Deox Reagent from Taylor. I retested the water but there was no noticeable change from yesterday. FC near 0, CC at 1.8. It appears MPS is not an issue with testing CC.

I bought an ammonia test kit. The reading was 4 ppm on the pool water. This can't be good.
I tried the bucket test. I put 2 gallons of water in a bucket and added 1/4 teaspoon of 6% (5.7% free chlorine) bleach. I then waited about 5 minutes for any magic to happen and measured FC = 4 (forgot to test CC). I then waited 2 hours and took more readings. FC = 1.5, CC = 1.0. I them added another 1/4 teaspoon of bleach, waited 5 minutes and took readings of FC = 22 (?? Sounds high, is kit accurate to that level ??) and CC = 1.5. I also took another ammonia reading which was an improved .5 ppm. However, the Ammonia test kit uses a solution that contains bleach so I suspect the reading may be off in water with high FC levels (unlike the aquarium water normally used with the test kit).

I waited 2 1/2 hours and tested the bucket water again. FC = 6, CC = 1.5, Ammonia = .5

I'm not sure what to make of all this but my understanding at this point is it will take 10 times the combined (ammonia + CC) to reach breakpoint on the pool. That would be (on pool water) 4ppm + 1.8ppm or 58 ppm. Does this sound correct? Should I buy enough bleach to reach 58 ppm or can I put in 5 gallons at a time until the ammonia is gone and then shock it with 10 times the CC?

Any other ideas?

Thanks

 

[duraleigh]

Should I buy enough bleach to reach 58 ppm or can I put in 5 gallons at a time until the ammonia is gone and then shock it with 10 times the CC?

I would like for you to define your CYA a little better before we get to that. You posted a pretty broad range for CYA. Can you be more specific?

 

[chem geek]

The ammonia reading implies that you'll need at least 30 ppm FC, but your bucket test seems to indicate you'll only need 10 ppm or so. Anyway, it looks like you won't need very much bleach. Though you could add it until you get a stable FC reading, Dave's point is that to know what final level you want your FC to be you'll need to accurately know your CYA level.

 

[FixRFill]

I took my pool water to two pool stores today for testing. The first store used an automated dip stick type test and gave the following results:
FC: .5
CC: Not given. Based on FC and TC it would appear to be 0 which I know is wrong.
TC: .5
Ph: 7.0
TA: 88 Note, it also gave an Adj. Total Alk = 73. I assume this is a correction based on the Ph and CYA levels.
CYA: 49
Hardness: 229

The other store used individual test vials. I would think this would be more accurate. Results are:
FC: .1
TC: .8
CC: .7
Ph: 7.3
TA: 78
CYA: 72
Hardness: 219

I measured the CYA and my guess using the black dot test is around 60. I'm never sure what the real endpoint is on the black dot test. I can always see the dot in some form. I assume they mean when the dot color blends in with its surroundings. Any help with how to interpret this test would be appreciated.

These CYA levels are quite a bit higher than the last time I tested it. Perhaps this is because I have been using a lot of Trichlor tabs in an attempt to keep the pool from getting out of control while trying to solve the FC problem.

Regarding the bucket test, I checked it this morning and FC = 0, CC = .8. I added another 1/4 teaspoon and FC = 16.5, CC = 1.0 and Ammonia = .25. As before, the FC shot way past the expected 10 ppm. Is it possible the bleach I have is considerably stronger than advertised? This may explain part of the inconsistency between the expected amount of beach needed based on the ammonia level and the results of the bucket test.

I'm curious about a couple of things. My basic understanding (and possibly wrong) is that chlorine should react with the ammonia to form chloramines which should show up as CC. So, why does adding chlorine appear to reduce ammonia levels without raising CC levels?

Also, I have read many places if you are shocking and don't get the FC level high enough to reach breakpoint, you have wasted your money and probably made the problem worse because the chlorine is just going to produce a higher CC. My (possibly stupid) question is, if you have a high level of CC that requires an unusually high amount of chorine to reach breakpoint, can you turn the pump off (at least initially) and put the estimated bleach amount in the shallow end to force a much higher initial FC level in the shallow water in the hopes of reaching breakpoint on some of the water if not all of it? This way you would at least make progress on it.

 

[rmklaw]

I am having a similar issue with FC one week after doing the AA treatment. I cannot get the FC above 0.5 no matter what I try. My readings this morning were:

FC 0.5
TC 3.0
PH 7.0 (I am letting it raise very slowly to avoid metal deposit reocurrence)
TA 107
CH 315
CYA 40
Salt 3000
Sequestrant 20 ppm

Yesterday I added lots of liquid chlorine, but it only raised the TC, not the FC. I am running out of ideas. Suggestions would be greatly appreciated. Thanks.

 

[FixRFill]

Thought I'd give an update.
Last night I shocked the pool with 9 jugs (182 oz each) of bleach. Two hours later I had FC level of 6 and the ammonia was around .25. This morning my FC level is back to .5. This pretty much matches my bucket test. But, at least I got above .5 for a while.

I have done quite a bit more reading (TFP threads) and it seems that it is time for me to raise my FC level to shock level (based on my CYA level) and attempt to maintain it until I can pass the overnight test.

Richard (rmklaw), I suggest you get an ammonia test kit and do the bucket test as I did. I am fairly confident the ammonia level was keeping my FC at .5.

 

[rmklaw]

Thanks. Good suggestion. However, I suspect that the residual ascorbic acid and Jack's magic Purple may be eating my FC. Finally today my pool water is almost clear. Today's readings are:

FC 0.3
TC 1.0
PH 7.2
TA 98
Sequestrant 10 PPM
Salt 3000

Still can't raise FC. Will keep adding liquid chlorine.

 

[Poolschoolgrad]

I regularly use Jacks magic purple to keep Iron stains from forming on vinyl. I have not noticed any reduction in chlorine when I use this product.

However, when I did the Ascorbic acid treatment I had to supplement the chlorine generator with bleach for about a week. I ran the SWCG on 100% for another week to keep the chlorine up. I slowly reduced the output %, but it took about two more weeks for the chlorine generator to get back to it's normal cycle.

The good news is the stains are gone.
Except for a small spot right between the main drains.

 

[frustratedpoolmom]

When oxidizing ammonia, the answer is more chlorine. So hang in there.

After an AA treatment, the chlorine demand is high, and you need to test and add small amounts 1-2 ppm up to hourly until the FC level beginns to hold, at your "min" FC level. What you are seeing is not at all unusual.

 

[FixRFill]

Well, I can now easily hold the FC to a decent level. It looks like I'm losing around 4-5 ppm of FC every 12 hours. I have company staying with me and the pool is a must so I can't keep the FC at shock levels. I am trying to keep it around 6 while they are here (until Wed.) as long as the CC levels do not drift above 1. I know this isn't exacly tfp guidelones but we will see how it goes.