Slamming for the First Time - Massive Chlorine Demand

[Jdub67]

Hello. My first post. It's long so skip to the bottom for my question if you don't want all the background.

I've had an in-ground pool for about 4 years now. This summer however, I haven't been able to hold any FC. I had been shocking it (though I had no idea what shocking really meant) quite a bit this summer with Bioguard Burnout (pool store recommendation). Even with the old test kit, I could see that my FC was too low. Eventually my pool started to show some algae growth on the walls and bottom that are more in the shadows and at night with the pool light on, we were getting all kinds of water bugs. My wife read online that Inhibit Back-up algicide would kill the algae and bugs. So we dumped in a bunch of this algicide. It didn't help. Though even during this time, the water didn't look too bad, after shocking and brushing it would get brownish cloudy, but I could always see the bottom of the deep end and after a couple of days it would look good again for a few days and then the algae would start showing up again.

Finally the pool store did a Chlorine demand test. They told me to drain my pool to a foot in the shallow end and refill (let the pump run for a while) and repeat and then shock it. I did this, but I still wasn't able to hold any FC. That's when doing some research on how draining the pool was supposed to help I found troublefreepool.

So even though my water never really looked too bad I decided I needed to SLAM my pool, but I didn't have a good FC/CC test kit so I ordered one, but wanted to start the SLAM anyway. At first I thought I was supposed to just add bleach in the morning and at night. I had the pool store check my CYA level before I started and they came back with a reading of 55. I hadn't really known what the CYA level was for before, so I then started going over the readings this summer from the pool store. They were all over the place, one time a 8, so they had me add stabilizer, then it went up to 89, then down to 40 then 55 when I last checked before wanting to SLAM. My FC was 0.5, CC 6.1, pH 7.6 and TA 130. So I made a guess that the 50 was my CYA amount and started the SLAM process on Saturday. So that weekend I added bleach enough bleach to bring FC up to 20 in the evening. Tested in the morning and FC was low and added bleach in the morning again to bring FC to 20. I repeated this every day: Sat, Sun, Mon, Tue, Wed. At first when I would brush the pool, it would always mix up some brownish junk, even after just a couple of hours on Sat/Sun. But by Wed, I could start to see that brushing wasn't mixing up as much stuff.

My Taylor test kit arrived on Wed so I started doing my own testing. FC 0.5, CC 1.5, pH 7.4, CYA 35, TA 135. I repeated the morning and evening shocking to, but to 16 now. But I had also re-read the SLAM process and determined that I was supposed to be trying to keep the FC at shock level each hour. So Saturday, I added 20 gallons of 8.25 Walmart bleach throughout the day when I was home, brushing the pool doesn't seem to stir up anything anymore. But each time the FC level would drop to 1 or 2 at most after a couple of hours. So today (Sunday) I decided to try to shock hourly as I didn't have anything else going on. I retested my CYA and now I think it might be about 35 (maybe didn't do the test quite right the 1st time?) So I've been adding shock all day to bring my FC up to 20 just to be safe. So for my pool that is just over 6 gallons (121 oz) of 8.25 bleach. Each hour when I do the reading again FC is down to 1.5 or 2. I'm 35 gallons in today and Walmart is out of bleach, so I had to go to the pool store to get some more 12.5% shock.

BTW- about by Wed, the pool was looking marvelous darling, crystal clear and my wife says it feels really soft. The vinyl liner feels clean and not slippery for the first time probably since we got the pool.

My question: Is it normal/OK to need this much bleach (35+ gallons in 1 day) and still not be able to hold any FC levels for a crystal clear pool? Is there something else besides algae (and the sun) that is consuming my chlorine?

Thanks for any input!

 

[duraleigh]

It certainly is OK but not normal. It may be ammonia in your pool but the way to get it out is more chlorine. Your path is simple and really without options. You need to put more chlorine in the pool until the demand starts to lessen. Sorry.

 

[Richard320]

That algaecide you used also uses up a lot of chlorine as it breaks down.
http://www.norflowinc.com/images/BioGuard_Back_Up.pdf

At some point soon, you'll get ahead of whatever it is -- ammonia, algaecide, algae -- and suddenly it will start holding FC. That's when you attack the lights and steps and anyplace else the remnants may be hiding and you'll be done in no time then.

 

[Jdub67]

Thanks Dave/Richard! I was just about to the point of giving up, because I wasn't seeing any progress. After Dave's post I almost ran out and got an ammonia test at PetSmart, but then finally my pool only went from 20 down to 6.5 in an hour, still a big drop but the first time I had been above 2 all day (all season probably!). So I shocked again to 20 and this hour I only dropped to an 18.5 FC and CC at 1.5! Making progress! I wish I would have known what my ammonia level was before I started all this. Would have been interesting to know how much chlorine it takes to get rid of ammonia in my pool. Anyway, I hope my slamming will be coming to an end soon and won't have to add quite so much chlorine to hold FC levels from this point on.

Might be a good idea to update the slamming page to note that you might have a clear pool and still need to slam because of ammonia. I didn't make the connection until Dave's post above.

Richard, looks like I'll be researching how to attack the lights and steps next!

Thanks for the support guys, like I said I was about to give up and I was so close. Just needed someone to tell me I wasn't wasting my time!!

 

[chem geek]

We know how much chlorine it takes to get rid of ammonia. If the ammonia test kit registers as ppm Nitrogen, then it takes roughly 8-10 times that amount as FC to get rid of it. The problem is that you'd have to measure the ammonia before you started adding chlorine to it otherwise you'll also be measuring monochloramine formed when chlorine and ammonia react with each other. Also, in most bacterial conversions of CYA into ammonia there is also partially degraded CYA and that won't show up in any test but will still need chlorine to oxidize it. So the chlorine demand will typically be higher than what an ammonia test or Combined Chlorine (CC) tell you. One way to know is to do a bucket test -- i.e. test adding chlorine to a bucket of pool water and scale accordingly for an estimate of how much chlorine it will take for the pool.

Another way of estimating is if you know the CYA drop since every ppm CYA drop takes roughly 3 ppm FC to oxidize the ammonia and degraded CYA.

 

[Accident]

Make sure you pull out the light and check/clean the housing behind it. Also check ladder steps (bottoms) and anything else that could be holding algae and not visible. May be fine, but worth not skipping. Really wish that was in slam instructions.

 

[Jdub67]

We know how much chlorine it takes to get rid of ammonia. If the ammonia test kit registers as ppm Nitrogen, then it takes roughly 8-10 times that amount as FC to get rid of it. The problem is that you'd have to measure the ammonia before you started adding chlorine to it otherwise you'll also be measuring monochloramine formed when chlorine and ammonia react with each other. Also, in most bacterial conversions of CYA into ammonia there is also partially degraded CYA and that won't show up in any test but will still need chlorine to oxidize it. So the chlorine demand will typically be higher than what an ammonia test or Combined Chlorine (CC) tell you. One way to know is to do a bucket test -- i.e. test adding chlorine to a bucket of pool water and scale accordingly for an estimate of how much chlorine it will take for the pool.

Another way of estimating is if you know the CYA drop since every ppm CYA drop takes roughly 3 ppm FC to oxidize the ammonia and degraded CYA.

Thanks Chem Geek. Guess I'm not the first one to wonder about how much chlorine it takes to get rid of ammonia. Great idea about the bucket test. Guess in the end it doesn't matter, but hopefully it would give someone an idea on how much bleach to buy up front!

Now that I seem to be holding FC (all day today), but when I do add bleach it doesn't seem to affect the color of the pool water at all. Before, when I was using up all my FC (by what I'm assuming was ammonia), every time I added bleach, the water would turn a brownish color for about 1/2 hour or so. I assumed it was just the inert stuff in the bleach making the water change color and the filter was clearing it out. But now I wonder if that was the reaction of the chlorine and ammonia, since now when I add bleach the water stays clear and doesn't turn brownish at all.

- - - Updated - - -

Make sure you pull out the light and check/clean the housing behind it. Also check ladder steps (bottoms) and anything else that could be holding algae and not visible. May be fine, but worth not skipping. Really wish that was in slam instructions.

Thanks Accident. I've never pulled the light before, so I'll have to research how to do that. I'm sure that is on here somewhere! I did pull the ladder out at the start of this because I thought that might be the source of the algae issue. Sow now that I think I have the algae issue somewhat under control, I'm going to have to disinfect the ladder separately. I probably should have just left it in the whole time so that it disinfected the same time as the rest of the pool. Live and learn I guess.

 

[Accident]

Kill breaker so you don't kill yourself. Look for Phillips screw at top middle of light. Unscrew it till out (might be able to do from deck if you lay down and have long arms). Lean top of light out and pull it up (probably will float up naturally. It has a little lip on the bottom that seats into a notch of the light housing in the pool.

Hopefully they ran enough cable that you can set it on the deck. Mine just barely makes it but some do not at all. Do not pull hard or at all on the cable. Once out (on deck or floating), brush out the area. I hosed it first on a jet setting with nozzle and it was ugly, then I brushed. You might have to get in to brush by hand.

Again, breaker off. Light should not be on outside of pool supposedly but more importantly you should not be touching it if there is power. Don't just do switch, full breaker off please.

Btw, some have a free washer on the back side of the light faceplate. Be aware. Also never hurts to kill the pump when doing things in your pool that may fall to the bottom and get sucked in by main drain.

 

[MarianParoo]

Even though I have great pool water, I get nasty algae occasionally behind my lights.

I set up my vacuum before I pull the lights and have my spouse ready at the multi-port. When I say "Go", spouse switches the multi-port to "waste" and I vacuum out the biggest crud from the niche. I wait about 2 minutes for all the gunk to get out of the vacuum line and yell "Done". Spouse switches back to filter. Then I closely monitor FC/CC just in case.

 

[chem geek]

Now that I seem to be holding FC (all day today), but when I do add bleach it doesn't seem to affect the color of the pool water at all. Before, when I was using up all my FC (by what I'm assuming was ammonia), every time I added bleach, the water would turn a brownish color for about 1/2 hour or so. I assumed it was just the inert stuff in the bleach making the water change color and the filter was clearing it out. But now I wonder if that was the reaction of the chlorine and ammonia, since now when I add bleach the water stays clear and doesn't turn brownish at all.

That's interesting and I don't know what that brownish color was from. I never saw that when I got rid of ammonia in my pool and I haven't heard this before in other threads that I can recall. Normally a color like that might come up from oxidizing iron in the pool but that would happen when adding chlorine that raises the pH. Instead it sounds like you had something that perhaps got colored from monochloramine. Or there was something else in the water. Strange.