Can't hold chlorine - no good reason?

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piku

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Mar 12, 2008
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Hatfield, PA
Hello guys,

Some of you followed my other thread where I got the pool clear. It was neglected for 3 years. During this process I accidentally shot the CYA way way high. (It WAS reading 0 :p ) Now I was told a couple things:

A: I need a better test kit to check chlorine - check - got duraleigh's FAS-DPD kit for chlorine. All other tests of walmart or Taylor K-2005C should be fine.
B: Only 2 things consume chlorine - organics and sunlight.

Well I went through the pool and took out every single little leaf, emptied the skimmer basket, etc. No apparent algae anywhere, water is clear and sparkling. AND it's dark outside.

Every time I test the pool it seems to be around .5 - 1 FC. 1-3 CC. No matter what I do, no matter how much bleach I add or how hard I shocked it. I'm preparing for a huge push on saturday bringing it to 25 and keeping bringing it to 25 (using probably 30+ jugs)...

Numbers:
FC .5
CC 1
PH 7.0
TA 170
CH 420
CYA 100 (maybe slightly more, not much)
Temp 52
phosphates 300
nitrates 2
no metals, etc
TDS 1000
17k-18k gallons, maybe less due to curved bottom.

So I add 2 jugs bleach. This should bring FC to 10. Now if there's algae blooming it's nascent at best. With my CYA so high the oxidation should happen more slowly and my FC should definitely come up. It's well after dark too. I leave for an hour and come home and use the kit. Same exact levels. This is with the pump running with main drain too.

HOW IS THIS POSSIBLE!? This happened the whole time I was shocking. The only way I finally managed to clear the pool was by adding 5 jugs bleach followed by 8 cups of trichlor which should have raised my FC to 48 ish. You'd think if I tested recently after adding that I would have a lot of chlorine reading but I didn't. I managed to clear the pool but I don't know how. *EVERY* time I tested, even an hour later I read .5 FC max.

The average uneducated person wouldn't worry but I need to understand what's happening here. Anyone have any ideas? The water temp is pretty cold, if algae is growing it's happening *really* slowly and showing *no* evidence.

I've tried adding bleach in front of hte returns or directly into the skimmer. No real difference in readings. I test by taking the leslies sample bottle, picking up water from 1.5ft down half-way between the 2 skimmers (kind of dead middle of the pool area). I get the water, bring it inside and test right away. Natural light isn't necessary for the FAS-DPD but even using my kitchen flourescent lights I can get relatively close numbers.

Please don't tell me to read the stickies, etc etc etc. I've read them... all of them. I've done my best to educate myself so if I'm doing something wrong, I need it specifically pointed out to me :)

I'm OK with buying 30 jugs of bleach at walmart despite the cashiers wondering what the heck I'm up to (I actually got laughed at by some teenager when I had a cart with 4 boxes of borax and the pool test kit) but I have to understand what I'm doing this for and if I'll succeed and what it will take to succeed. There MUST be a limit to this.

I'm really feeling the walmart 6% is either old stock wiht no potency or fraudulent.

Tonight I'm probably going to go get walmart bleach and test it in controlled conditions to see if I get the FC rise I think I should.
 
My best guess at the moment is fertilizer. If some fertilizer got dumped, or washed, into the pool it would account for your experience. It can take dramatic amounts of chlorine to clean up after fertilizer.

Now would be a good time to do an experiment. Get a five gallon bucket of pool water and add one oz of bleach at a time and mix and wait a little while and then test the FC level. For each teaspoon of bleach you add to the 5 gallon bucket before it starts holding a FC level you are going to need to add 96 ppm of chlorine to the pool. If one oz clears up the bucket you can do it again with teaspoons and fresh pool water, each teaspoon in 5 gallons is about 16 ppm of chlorine.
 
Piku, like I say before, I'm following your thread closely to learn more.

Yeah, Jason just hit it. I was thinking the same idea but have to refresh my memory from your other thread and by the time I'm back, Jason already got in. That test will determine at least 2 things (I think). Keep the bucket away from direct sunlight to see if CYA is a culprit. The other is whether anything else keep getting into your pool (can be air borne or even any leakage into your pool from under your decking etc). Keep the bucket away from the open from airborne contaminant. Compare the resulting numbers.

Just a beginer's 2 C.

Vincent
 
I would think my nitrates would be super high if fertilizer got in. I know that's a primary component of fertilizer. The only thing untested is ammonia. I wonder if it's possible that the algae living in there for years has ended up creating a ton of ammonia. I think we can all agree that bucket based testing is the only way to take care of this (or at least figure out what amount of chlorine and $ amount roughly this will take).

Like I said, I'm all for spending money, but I really like predictability, planning and understanding :p
 
If you originally had CYA in the pool with no chlorine (such as happens when a pool is "let go"), then soil bacteria (that blew into the pool) can use it as food and convert it to ammonia (the degradation pathway is shown here). Every 10 ppm of CYA that degrades produces an amount of ammonia that would quickly combine with 16.5 ppm FC that was later added to produce monochloramine which would register as CC. It takes at least a further 9 ppm FC or so to oxidize the monochloramine. Since you're not seeing much CC, I'm not sure if this is what's going on. You'd probably smell the monochloramine.

So if a pool had 100 ppm of CYA initially and it all degraded to ammonia, then it would take over 250 ppm FC cumulatively to get rid of it. That would be pretty extreme. Ammonia is more volatile than chlorine so unless the water was very cold the ammonia would normally be expected to dissipate over time.

I believe you can get an inexpensive ammonia test at any place that sells aquarium equipment (waterbear would know more about that). I'm not sure if the test works if there's chlorine in the water. Jason's bucket test is also a good way to find out how much chlorine it takes before it holds, regardless of what's actually in the water and I suggest you try that just to see what the chlorine demand really is.

At the end of the day, the lesson learned here may be that if a pool is let go for years, it may be better to drain/refill if the water is in really bad shape. The bucket test will tell you how much further you have to go and then you can decide what to do at that point. With the high CYA, you might opt for some partial drain/refill, but do the bucket test first.

Richard
 
Maybe - but I have my doubts on the drain and fill. You still have to scrub it considerably and then you have a potentially new pool owner worried about floating the shell. Also in my case, my equipment was non-functional and was so for days. If you immediately do a drain and fill you don't get to learn about your equipment problems irrelevantly dirty water, but you have clean fresh water you want to get moving right away. Vacuuming all the crud out is probably far easier with water in it. I feel that this has all been a great learning experience for me learning about chlorine, equipment, etc. What if you do a drain and fill and come to find you have a main drain problem which necessitates another drain and fill? :p Though I think 18000 gallons of city water is only a little over $20 - so when you're talking about exact expense of fighting unknown contaminants - the writing is on the wall for the path I took.

When I say considerable expense, I do mean it as a new home owner. $100 versus $20 is important to me but the bottom line is that I don't think I've spent more than $75 or so on bleach. We're not "out of the ballpark" in terms of expense yet but it is working on it. My feeling is that I am close to finding an end to the FC consumption but tonight I'll bucket test and find out for sure.

The one thing you say is interesting- that the ammonia could be expected to dissipate over time. Many people find that the CYA is gone after one winter due to the bacteria consuming it. This pool was closed for several summers so the CYA consumption happened and is gone. Plus I know of people who used pond water for their pool and that's more or less what I had. So it could explain the ammonia or not. Does algae germinating and dying produce ammonia or compounds like that? I need to go back and count but I've added I think 35 jugs total of 174oz ultra which would put me up to around 160FC. Add to that copious amounts of trichlor and dichlor (which may have lost some effectiveness but certainly increased my CYA without a problem).

I wonder if I should submit my water to a real lab and ask them. I bet they could figure it out pretty quickly but that would cost more than the chlorine :p
 
It is not unusual for a pool to have a huge chlorine demand when it's been unattended for a while. Usually ammonia, urea, and other nitrogen compounds are the culprit. Your test was only for nitrates BUT there ARE other species of nitrogen compounds that can be in your water. Since you have a plaster pool you can safely 'nuke it' with chlorine. This often help. Bring your FC up to about 50 ppm and leave the pool uncovered until the FC drops back down.

The other possibility is that your CYA is actually a LOT higher than you think since it becomes very difficult to accurately test CYA above 100 ppm without doing dilutions. This would mean that you are just not getting the FC high enough to reach breakpoint. I suspect that this is also coming into play here.

A final possibility is that your pool is bigger than you think it is and you have been underdosing the whole time.
 
I wonder though. If I put in 2 jugs a day (or whatever) to continually bring it back up to 10 (or whatever) woudl that be just as effective battling nitrates, urea, ammonia, and other non-algae things as breakpoint chlorination or does "shocking" or breakpoint chlorination make the process happen far more quickly. I could understand why you would want to shock to kill algae but since this is a different animal I wonder if the same rules apply. I probably still have 1 CC because I can't get my FC to proper shock levels because it gets consumed so quickly.
 
The big advantage of going fairly quickly is that left alone for 24 hours without FC the pool will get at least a mild case of algae and then you will end up fighting the algae each day, reducing the amount of chlorine going to deal with whatever else is going on.
 
piku said:
I wonder though. If I put in 2 jugs a day (or whatever) to continually bring it back up to 10 (or whatever) woudl that be just as effective battling nitrates, urea, ammonia, and other non-algae things as breakpoint chlorination or does "shocking" or breakpoint chlorination make the process happen far more quickly. I could understand why you would want to shock to kill algae but since this is a different animal I wonder if the same rules apply. I probably still have 1 CC because I can't get my FC to proper shock levels because it gets consumed so quickly.
Click to expand...
no because you would not destroy all the ammonia and nitrogen compounds in the water but only create more CC. You need to nuke the pool. 10 ppm is NOT going to cut it, expecially with CYA over 100 ppm!
 

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I bought 2490 oz of 6% from walmart tonight. Worth 67ppm FC. I'm going to stop by Aldi tomorrow and see what they can do for me. I read elsewhere that they have 1 gallon bottles for $.99... a steal compared to the prices I am paying. I paid $35 for the walmart chlorine. I only home that it HOLDS and doesn't consume all 50 ppm and laugh at me and my money!
 
piku said:
I'm going to stop by Aldi tomorrow and see what they can do for me. I read elsewhere that they have 1 gallon bottles for $.99... a steal compared to the prices I am paying.
Click to expand...

We use Aldi's bleach. It is NOT one gallon, it is 96 Ounces = 3 QTS....but is still our best buy in town. Good luck.
 
Hrmmph. I came out today after a hard rain and there were around 30 earthworms in the pool. 3-5 in the shallow section and about 25 hovering near the main drain. A few of them alive. Now I don't know if earthworms go 10ft down but I figure they probably do and I figure they probably came up into the pool because they saw light that way due to some sort of HOLE. Now if my neighbors use fertilizer and ground water is exchanging with pool water a bit, that might explain a whole heck of a lot. (as posted in another thread, my main drain blows bubbles!). I can't say with any certainty that the worms came from the drain because they could have come into the top seeking the ground and all went down to the deep end. I didn't witness what transpired. I can say that if there's a leak in the main drain, it's right there, right at the cover and probably repairable.
 
waterbear said:
piku said:
I wonder though. If I put in 2 jugs a day (or whatever) to continually bring it back up to 10 (or whatever) woudl that be just as effective battling nitrates, urea, ammonia, and other non-algae things as breakpoint chlorination or does "shocking" or breakpoint chlorination make the process happen far more quickly. I could understand why you would want to shock to kill algae but since this is a different animal I wonder if the same rules apply. I probably still have 1 CC because I can't get my FC to proper shock levels because it gets consumed so quickly.
Click to expand...
no because you would not destroy all the ammonia and nitrogen compounds in the water but only create more CC. You need to nuke the pool. 10 ppm is NOT going to cut it, expecially with CYA over 100 ppm!
Click to expand...

With a gunite pool, having a CYA of 100+ you cold hit a chlorine level of 20-25 and not harm the gunite. Golly, 10ppm is WAY TOO LOW! Also, maintain constant filtration and you'll be seeing clearing shortly. Just make sure that you are maintaining the higher chlorine level throughout the day. Yo-yoing will prolong the battle.

CaryB
Go 'Canes
 
Okay, no ammonia test strips yet but I've been doing some experiments today.

I took 5 gal pool water into a bucket and have a plastic stir stick.

I added 3 tsp 6% bleach which is roughly 45ppm FC.
I tested 1 hour later and had 3-5.
Added 2tsp and 1 hour later had 2.
Added 3 tsp again
checked in 5 minutes and had 17ppm
checked in 1 hour and had 7 ppm
added 3 tsp again

So I have instant consumption as well as long term consumption.

The other numbers have changed drastically due to rain
TA 130
CH 325
CYA 100

I have to go do my 5 minute check now but I still don't see an endpoint to the chlorine consumption.
 
Checked again after like 20 minutes. 37 PPM FC which means it consumed about 15 ppm in 20 minutes.
10PPM CC...... so still didn't break it!!
27PPM one hour later (10PPM in 1 hour). Next check tomorrow morning.

This is equivalent to 32.8 174oz jugs of 6% ultra bleach... I have just 13 in the garage and that alone is $30something. I calculated full drain and fill:

18000 gal, 100 ft3 of water is $3.05. 750 gallons of water in 100ft3 which is $73.20.

I've already partially drained and filled it too. Today I was vacuuming to waste and took it well below the tile line, then refilled it but it didn't seem to affect my CYA (my other levels vastly shifted though). My lovely discharge hoses from leslies exploded and flooded my front yard. Can anyone recommend a place to buy decent 150ft discharge hose that WON'T break so easily (and yes I was quite careful with it).

The most obnoxious thing is that the pool is clear and beautiful. I'm fighting an invisible enemy.
 
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