Mysterious chlorine loss... SLAM even though not failing entrance criteria?

Jump to latest Follow Reply
TriangleMan

TriangleMan

Well-known member
May 30, 2021
78
Lake Barrington, IL
Pool Size
25000
Surface
Vinyl
Chlorine
Liquid Chlorine
I completed a SLAM three days ago, including passing all three criteria (water is clear, CC=0, OCLT dropped only 1ppm), but my Chlorine loss is higher than I'd expect.

I needed to add 4ppm to the water a couple days ago and 8 ppm to the water yesterday. I've had a heavy bather load with a many as 7 kids under age 9 a couple days ago, and 5 yesterday, so I attributed it to them, plus the sun in our almost completely unshaded pool.

The posts I've seen about chlorine consumption don't put the loss to the sun (2-4ppm), Bathers (0.04 ppm / person-hour for a pool this size (25kgal)), or even urine (0.06ppm per cup of urine in a pool this size) high enough to account for the losses.

To be sure, I ran an OCLT and failed this morning. (5 ppm down from 7 ppm).

But the water is clear, FC has been at or above the minimum for my CYA = 40 (except once that I measured 2ppm after the 7 kids were swimming and immediately added chlorine to get to 6ppm) and certainly never hit zero (I've been keeping it near the maximum recommended 7ppm), there is no algae, and CC has consistently been <=0.5ppm since completing the last SLAM three days ago.

So my question is should I SLAM based on failing an OCLT even though I'm still passing the entrance criteria of FC>0, CC<=0.5, and no algae?

Not sure where else the chlorine could be going...

FC 5
CC 0.5
PH 7.7
TH 200
CH 325
CYA 40
 
Last edited:
If you fail the OCLT you need to SLAM. There are 3 criterion. If you fail any of them you need to SLAM.

My guess is you ended your last SLAM too early and were not really complete. A best practice is to keep the pool in SLAM level for one or two days after passing the SLAM just to be sure. During that time super brush everything especially lights, and skimmers.
 
  • Like
Reactions: Mdragger88, TriangleMan and newdude
Hey TM !!! Go on an algae treasure hunt looking for anywhere it was hiding in plain sight. Ladder rails for example look fine but could be holding 2 gallons of old water on each side. Skimmers, weir doors, steps, really anything at all needs a good once over to make sure you got it all.
 
  • Like
Reactions: TriangleMan
I'll go with the assumption that I should have held the SLAM another day or two, but I thought of another possibility as well. Some of those kids came over from another house that has a pool. Let's say that pool isn't maintained to TFP standards and has algae in it, which would be carried over to my pool on their swimsuits. Is that a concern? I would think that the point of having an FC level on the high end of the FC/CYA chart should be sufficient to fight off intruders like that (or perhaps even stray algae that missed the brush in my own pool at the end of the SLAM)...

I struggle a bit to understand how the pool is so easily susceptible to continued algae growth after starting from a solid point (passing a SLAM).

I've raised up my FC level to 17 and will monitor the SLAM once again.
 
If you SLAM was not complete (lets go with that). Then your pool was already fighting algae which at anything under SLAM is usually a losing battle. Keep the pool in SLAM level for 2 days after you pass. Then stay at the high end of the FC/CYA level and life will be good.

Dont worry about bathing suits with algae on them if you FC is high it will deal with with. But you need to be clear first.
 
  • Like
Reactions: TriangleMan
triangleman3 said:
TFP standards and has algae in it, which would be carried over to my pool on their swimsuits. Is that a concern? I would think that the point of having an FC level on the high end of the FC/CYA chart should be sufficient to fight off intruders like that
Click to expand...
Exactly. High end FC would easily kill off a little extra. And the ‘little extra’ described would be like spitting in the ocean in reattach to your 25k gallons.
triangleman3 said:
I struggle a bit to understand how the pool is so easily susceptible to continued algae growth after starting from a solid point (passing a SLAM).
Click to expand...
Easily by 2 ways. Either you really needed one or two extra days to be fully clear, or it was hiding somewhere in plain sight. So you passed and started round 2 almost immediately. Go after both and be done. :)
 
  • Like
Reactions: clambert1273 and TriangleMan
Looking for reassurance? I feel like I'm dumping a tremendous amount of chlorine into the pool, and I'm not sure if it's really benefitting anything.

I've been doing a SLAM since Friday 6/11, as mentioned above, which is a continuation of a SLAM that I must not have completely ended the week prior. I resumed it based on observed FC loss.
The water has looked clear the entire time, at least from above looking down into 8 feet of water. From inside the pool, looking across 40 feet of water towards the light at the deep end, I would say it's not crystal clear, but not normally something I would have thought to complain about before TFP.

I've been holding the FC at 16 as often as possible (refreshing chlorine at least 4 to 5 times a day), hand-scrubbing, brushing (any recommendations on a good pole? I've bent this one twice now... I guess I don't need to brush that hard), vacuuming, etc., even though there is no to very little dirt visible.
I've been seeing FC drop 2-4ppm between tests spaced 2 to 4 hours apart throughout the day (if I'm trusting my memory; I need to start writing this down). I haven't run an OCLT lately because I feel like the daily chlorine loss still seems too high to warrant looking for the end criteria.

Today I decided to remeasure CYA, and I suppose I'd consider it 50ppm. (It's so subjective that it's hard to tell. I believe I can make out the dot even at the 30 ppm line, but it takes much more than a quick glance. At 40 and 50 it's more questionable what determines a well-formed dot vs a dot that has disappeared; it's somewhere in between. In any event, it's certainly very clearly visible at the 60ppm and in my subjective opinion visible at 50 but maybe not really at 40).

Bumping up the chlorine level to target 20ppm FC for a 50ppm CYA, I feel like I'm just seeing chlorine disappear even faster. In the space of the last 6 hours, I've added about 14ppm to keep up with the higher FC target.

If the CYA is not actually at 40 or 50, I may just be sacrificing chlorine to the sun god, and if it's really at 30, then I feel like I'm throwing in way too much chlorine and risking my liner and the health of swimmers...
If it really is 40 or 50, then I might have thought that I'd see a similar consumption of FC ppm regardless of CYA level (i.e. it wouldn't have started consuming 2ppm/hr just because I'm starting from 20ppm if it was only consuming 1ppm/hr when I was starting from 16ppm)

Am I doing this right?

If I am mis-measuring CYA, or if I wanted to knock out the Algae faster, is there a FC level above the recommended FC/CYA relationship (40%) that is still at least safe for the liner and pool equipment, even if not safe to swim in? (For example, maybe I can go above the FC/CYA level at night when there won't be any swimmers, to speed things up, or, as I said, in case I'm wrong about the CYA level).

I haven't done a controlled experiment on the liquid chlorine itself to see that its strength is as advertised... so there's at least one loose end, but maybe that's a long shot.
Maybe I've also been wasting my time targeting FC 16 thinking CYA was 40 when my latest test says 50... but hopefully that just means the SLAM goes slower but still progresses.

Sorry for rambling... So many doubts...

(In the back of my mind, I'm also worried about the CH level and calcium scaling, which I feel I've gotten smarter about testing so as to see a defined endpoint [adding titration drops prior to the buffer/indicator to bind the copper in the water], especially since I have no idea how high pH might really be the entire time I'm doing this SLAM)

FC 15 (one hour after adding 8ppm after measuring 11... so I guess I'll throw in another gallon...)
CC 0.5
PH 7.8
TH 175
CH 425
CYA 50

As always, thanks for the insight team... I hope to become a true believer, once I can prove to myself this works...
 
Last edited:
With cya its better to round up & dose for the higher of 50ppm as there’s really no in between so hopefully you will gain some ground there.
Have you checked the date code on your bleach? It could be old stock or just could have been stored improperly & lost potency. Dose & then check again in 30 minutes to see where it got u to rule this out/adjust dosing. Like stated above check every where for algae- it likes to hide. I had a slam drag out because i left one of those diver toys in the pool & the end was filled w/ algae. I removed it & that night i passed my oclt. My water had been crystal clear pretty much the entire time.
 
  • Like
Reactions: TriangleMan
For the cya test the easiest way I have found is pour to line, glance at waist if I clearly see the dot then fill to next line and repeat, when I reach the point of glancing and the dot is no longer glaringly visible on my glance thats when I call it.. if I have to look hard for it then im done
 
Its a pool not a drinking water treatment plan. So if you miss a little and run a little hot, its not the end of the world. Dose for 50ppm of CYA which is FC of 20. Make sure you dose enough on your last dose, as there wont be any sun to consume it just the organics.

Here is a recommendation for a pool pole. It is a little pricey, and kind of heavy. But really strong. I think you can use it for pole vaulting if necessary.

specialoffer.protuffproducts.com

Get 10% Off a ProTuff "Lock Right" Pool Pole

The pole that "Always Grips & Never Slips" - Lifetime guarantee, unlimited NO COST replacements, rock solid performance
specialoffer.protuffproducts.com specialoffer.protuffproducts.com
 
  • Haha
Reactions: TriangleMan

Enjoying this content?

Support TFP with a donation.

Give Support
You’ve definitely passed the crystal clear part of the 3 criteria to end slam.
Have u checked the drain covers & does the slide have water to it? If so check that too.
 
Thanks for the pole recommendation!! and to everyone for the CYA tips. I'll do my best.

I use a hand scrubber to get areas that I feel the standard large pool brush can't handle, including the drain covers, underwater light, in the skimmer, including underneath and around the basket, and around the returns. I even use the hand scrubber to go around corners and edges underwater where the brush probably isn't making good contact.

I haven't done the slide, admittedly, because it's dry most of the time and has no visible crud. I don't take off the drain covers and get "inside" them though, nor do I remove the light from the wet niche. That seems like it'd be going a bit too far. I figure if that's a problem, how could I ever get to algae inside the plumbing or the flooded but stagnant conduit that leads to the light switch?? At some point can't I trust the chlorine to take care of the rest? The example of the pool dive toy causing a failing SLAM suggests this process is very very sensitive.
 
The drain is less likely, but a light niche is a great hiding spot for algae. Not very good water flow. Very often when people unscrew the light from the niche a ton of crud comes out. I would start there.

For the drain you can put a high pressure nozzle on a hose and just go down and try to flush it out. I would also suggest putting some LC in a plastic bottle you can cover with your thumb. Go down there and dump the LC down the drain after you flush it with the hose. That should take care of any nasties.
 
  • Like
Reactions: Mdragger88
Newdude said:
You pull the ladder amd drain it right ? Otherwise that water is just seeping out slowly. (y)
Click to expand...

uhh... nope... I haven't done that... I'll put it on the list.

Katodude said:
Its a pool not a drinking water treatment plan.
Click to expand...

... but I feel like it's getting pretty darn close... o_O
 
  • Haha
  • Like
Reactions: clambert1273 and newdude
triangleman3 said:
Looking for reassurance? I feel like I'm dumping a tremendous amount of chlorine into the pool, and I'm not sure if it's really benefitting anything.

I've been doing a SLAM since Friday 6/11, as mentioned above, which is a continuation of a SLAM that I must not have completely ended the week prior. I resumed it based on observed FC loss.
The water has looked clear the entire time, at least from above looking down into 8 feet of water. From inside the pool, looking across 40 feet of water towards the light at the deep end, I would say it's not crystal clear, but not normally something I would have thought to complain about before TFP.

I've been holding the FC at 16 as often as possible (refreshing chlorine at least 4 to 5 times a day), hand-scrubbing, brushing (any recommendations on a good pole? I've bent this one twice now... I guess I don't need to brush that hard), vacuuming, etc., even though there is no to very little dirt visible.
I've been seeing FC drop 2-4ppm between tests spaced 2 to 4 hours apart throughout the day (if I'm trusting my memory; I need to start writing this down). I haven't run an OCLT lately because I feel like the daily chlorine loss still seems too high to warrant looking for the end criteria.

Today I decided to remeasure CYA, and I suppose I'd consider it 50ppm. (It's so subjective that it's hard to tell. I believe I can make out the dot even at the 30 ppm line, but it takes much more than a quick glance. At 40 and 50 it's more questionable what determines a well-formed dot vs a dot that has disappeared; it's somewhere in between. In any event, it's certainly very clearly visible at the 60ppm and in my subjective opinion visible at 50 but maybe not really at 40).

Bumping up the chlorine level to target 20ppm FC for a 50ppm CYA, I feel like I'm just seeing chlorine disappear even faster. In the space of the last 6 hours, I've added about 14ppm to keep up with the higher FC target.

If the CYA is not actually at 40 or 50, I may just be sacrificing chlorine to the sun god, and if it's really at 30, then I feel like I'm throwing in way too much chlorine and risking my liner and the health of swimmers...
If it really is 40 or 50, then I might have thought that I'd see a similar consumption of FC ppm regardless of CYA level (i.e. it wouldn't have started consuming 2ppm/hr just because I'm starting from 20ppm if it was only consuming 1ppm/hr when I was starting from 16ppm)

Am I doing this right?

If I am mis-measuring CYA, or if I wanted to knock out the Algae faster, is there a FC level above the recommended FC/CYA relationship (40%) that is still at least safe for the liner and pool equipment, even if not safe to swim in? (For example, maybe I can go above the FC/CYA level at night when there won't be any swimmers, to speed things up, or, as I said, in case I'm wrong about the CYA level).

I haven't done a controlled experiment on the liquid chlorine itself to see that its strength is as advertised... so there's at least one loose end, but maybe that's a long shot.
Maybe I've also been wasting my time targeting FC 16 thinking CYA was 40 when my latest test says 50... but hopefully that just means the SLAM goes slower but still progresses.

Sorry for rambling... So many doubts...

(In the back of my mind, I'm also worried about the CH level and calcium scaling, which I feel I've gotten smarter about testing so as to see a defined endpoint [adding titration drops prior to the buffer/indicator to bind the copper in the water], especially since I have no idea how high pH might really be the entire time I'm doing this SLAM)

FC 15 (one hour after adding 8ppm after measuring 11... so I guess I'll throw in another gallon...)
CC 0.5
PH 7.8
TH 175
CH 425
CYA 50

As always, thanks for the insight team... I hope to become a true believer, once I can prove to myself this works...
Click to expand...
Using 2-4ppm of FC per day is pretty normal, not sure about per hour though. Definitely use the OCLT to judge and not daytime consumption.
 

Enjoying this content?

Support TFP with a donation.

Give Support
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply