Shocking and CC readings

[jmlodin]

I am currently doing a shock to the pool. I am testing FC and adding more bleach every hour according to the pool calculator. The FC is slowly rising but the CC is not moving much. Will it eventually go down as FC goes up? Do I even need to be measuring CC at this point or just the FC to get it to the shock level?
Thanks.

 

[duraleigh]

Well, you're on the right track. Actually I would word it like this...

Keep your FC at shock value by replenishing with chlorine as often as you can.....almost hourly at first and then you will find the chlorine dropping more slowly so you will only need to add to get back to shock value a couple - three times daily. The important thing is to keep replenishing the chlorine at that high shock level because........

that's what will ultimately get rid of your CC's. They may never come down to a complete zero but a test result of .5cc'c is considered zero for the purposes we use here on the forum.

1. I would not bother measuring cc's just now. do it later when your chlorine is starting to hold it's value.

2.

The FC is slowly rising but the CC is not moving much.

Explain the FC part of that sentence a little more. I would like to see the FC brought to shock value all at once and then you wait (for a few hours at your point in the process. Then you retest and add enough chlorine to get back to the exact shock value you started with.....is that what you're doing?

3. How have you calculated your shock value? Have you tested for CYA and, if so, post that result?

 

[jmlodin]

Thanks for responding since I really need the help! Ok I will start with the CYA. I tested yesterday with my new Taylor kit and got a reading of 50 but the water is cold at about 55 degrees. I retested this morning with a sample I let get to room temperature and the value was 40. I am using the calculator each shock to figure out how much 6% chlorine bleach to use. I have used a LOT so far! This morning at first test FC was 2, I shocked checked an hour later and it was FC 7.4, shocked again and it was 8.8 just checked again and it is only 9. I am using the calculator with 16 as my goal for FC. What am I doing wrong? I am going to wait to hear back before I shock again.

 

[257WbyMag]

Doesn't sound like you are doing anything wrong. Each time you check your FC, assuming that you are checking at the same time after the addition of bleach, you are getting a little bit higher residual value than you did before. This likely means that you are making progress.

Depending on the level of organics in your pool, your FC can be consumed fairly quickly, within minutes sometimes. You have been dutifully bringing your pool to an FC of 16 ppm each time you add and it seems to be working. The process is complete when you notice that the FC doesn't really budge much after time.

Keep bringing it to 16. Once it stays around there, you're good to go.

How's your water looking?

By the way, are you doing the 25 ml test sample of water when checking your FC? Since you are getting values to the nearest 0.2 ppm, I assumed that you probably were. Since you are shocking and working with really large values, you might save on some of your R-0871 Titrating Reagent by testing using the 10 ml sample. Your values will be to the closest 0.5 ppm but it will do you fine for shocking purposes. Just a thought. :-D

 

[duraleigh]

What am I doing wrong?

257 has the answer....you're doing fine. Like many of us when you first learn this, you are being surprised by just how much chlorine it is taking to sanitize your pool. Just think how many organics it is killing (even tho you can't see many of them.)

Stick with it. It is helpful to understand that clearing a pool is a process....not a one-time event. That process may take a few days more but your making progress. Watch the psi on your filter.....it may soon be time to backwash. Is the psi higher than before you started shocking?

 

[jmlodin]

The water does not look cloudy at all, maybe just a little hazy. The psi gauge has not moved since yesterday but maybe I will backwash anyway. Yes I am "shocked" at the amount of chlorine I am using and not getting to FC 16. I was using the 25 ml but switched to the 10 ml on the last test because I am going through test chemicals very fast. I am unsure how much of the powder to be putting on the dipper when I add two of them. Does it have to be a precise amount? It could be heaping or just a little, sort of unclear. I just try to use the same amount each time.

I was reading the taylor booklet about breakpoint chlorination. It says to take my CC reading x 10 and shoot for that number on a shock. My CC is still 3.5 so that would be a ton of chlorine all at once but maybe that would wipe out the CC value. What do you think?

 

[duraleigh]

I was reading the taylor booklet about breakpoint chlorination. It says to take my CC reading x 10 and shoot for that number on a shock. My CC is still 3.5 so that would be a ton of chlorine all at once but maybe that would wipe out the CC value. What do you think?

That would be a FC of 35ppm, of course. It will not hurt and will speed the process a little but you can accomplish the same just by replenishing to 20ppm. Some folks are nervous about putting that much chlorine in one dose in a pool. In your case, it won't hurt anything except, unfortunately, your wallet.

As long as the solution turn pink and stays pink, it's enough powder. Two level Taylor scoops usually works fine but you might try a little less.

 

[257WbyMag]

Yes I am "shocked" at the amount of chlorine I am using and not getting to FC 16.

If you are using The Pool Calculator and you are adding the amount of bleach that the calculator returns in value, assuming you have calculated your total gallons of water correctly, you aregetting to 16 ppm. It's just that by the time you get around to testing it, part of it is already consumed by the organics and has become CC. You're doing it right!

 

[Guest]

The exact amount of DPD powder is not critical as long as you are getting the pink color and it's not disappearing after a few seconds. If it does add another scoop.

 

[jmlodin]

I am really at a loss about what is going on with my pool. We decided to go the breakeven chlorination as suggested in the Taylor booklet to get rid of CC. Our CC was 4.0, so we calculated the amount of chlorine needed to get to 40 ppm. Went to the pool store and got 12% liquid chlorine. We added 7 gallons which was a little more than calculated. Tested after one hour and got these results which make no sense to me.
FC 4.5
CC 6.5
Instead of massively reducing the CC value it went up.
Not really sure what to do or what this means. Very frustrating.

 

[chem geek]

Did you just recently open your pool? If so, did you find that the CYA had dropped over the winter? If so, then what may have happened is described technically here (and also here) under "CYA Degradation by Bacteria" where soil bacteria get into a pool that has no chlorine and they multiply and consume the CYA. For every 10 ppm CYA, they produce 3 ppm ammonia and this takes 24-30 ppm FC to get rid of it. In practice, some of the ammonia dissipates (either outgasses or gets taken up by algae). When you add chlorine to a pool that has ammonia, at first it raises the CC and the FC fairly rapidly goes to zero -- it seems like an insatiable chlorine demand. At some point, the FC starts to measure but there is still CC which may be where you are at now. Then, the CC drops and the FC stays stable when you add more.

If you find this situation when you open a pool, you can get an ammonia test kit at a pet/fish/aquarium store and then use 8-10 ppm FC for every 1 ppm of measured ammonia.

The 10x rule that Taylor and others talk about to get rid of CC is technically incorrect. It is based on needing about 10 times the ammonia ppm reading. CC is measuring monochloramine (mostly) and in different units (ppm chlorine gas, not ppm nitrogen). The actual amount of FC needed to get rid of CC is only a little more than half of the CC level. Using more chlorine makes it go faster, but in your situation, you probably still had ammonia in the pool that would form more CC as you added more chlorine.

At this point, I'd just keep adding more chlorine until it FC holds at some shock level, at least 10 ppm or so. If you want to get an ammonia test kit, you can do that, but you might be at the point where all the ammonia is now used up and has formed CC.

Richard

 

[jmlodin]

This is starting to make some sense. We did open our pool last week and had it tested, the CYA was 0. We added conditioner to get that number up. Today we have put in over 100 ppm of chlorine throughout the day. So based on your advice we will continue to add chlorine and keep testing FC every hour. My question is how much bleach to add each time. Would I use the calculator like today and aim for 16 or 20 as a shock value based on the FC at the time?

 

[chem geek]

Well, quite frankly, you might seriously consider getting an ammonia test kit because if there is still a lot of ammonia in the pool then you might be better off doing some partial drain/refill. You say you've added over 100 ppm FC cumulatively so far. That would take care of ammonia produced from around 40 ppm CYA. If your CYA level at the start of winter was in that ballpark, then you are near the end. However, if your CYA was more like 80 ppm, then you've possibly gone around halfway (though could be further along if some of the ammonia got lost through other means).

If you just want to keep adding chlorine, then yes, use The Pool Calculator to figure on 15-20 ppm FC to add at a time, wait an hour or so, then measure to see where you are at. It takes a few hours to fully break down CC so if you measure too soon after addition, this won't be a good judge. Also, if there is ammonia in the water, then that raises CC almost immediately and lowers FC to near zero. So the fact that you are now measuring some FC in the water is a good sign and may mean you are nearing the end and could be just 10 ppm FC away. I've got my fingers crossed.

Richard

 

[jmlodin]

Thank you so much for your expertise. Here is where we are today. We tested this morning and FC was down to 1 again. We also bought an ammonia test kit and came up with a reading of .5. So we did a large shock again and tested an hour later, the FC was 10. We decided to shock again and tested an hour later and it is now FC 15.5. Retested the ammonia and it was 0. Maybe we have gotten through. We hope so! We are now going to wait a couple of hours to check FC and CC. Should the CC now be nearly gone?

 

[chem geek]

Yup, it does sound like you are near the end. 0.5 ppm ammonia would take around 4-5 ppm FC to get rid of. You will measure CC for a short time, but within 24 hours it should be near zero. If it isn't, but there is still substantial FC, then the CC isn't a simple chloramine but something else that might take a while to get rid of or may not go away (without dilution). I wouldn't worry about it unless it is tending to consume FC overnight in which case maintaining a shock level will help break it down faster.

Be sure to keep the pool open (airing out) during this process since the by-products are volatile gasses you want to escape (mostly nitrogen gas, but some small amount of dichloramine and nitrogen trichloride as well).

Keep us posted.

By the way, out of curiosity, what was the CYA level when you closed the pool?

Richard

 

[jmlodin]

We had a CYA of 90 at the end of September and were dealing with a "chlorine demand" according to the pool store. We put in a huge amount of granular chlorine and it cost us a lot of money and I don't really think it took care of the problem. We closed the pool mid-October and it was barely clear at the time. Now that we have found this site we are looking forward to clear water with less chemicals. You mention to leave the pool open. We have an auto cover that we always close at night. Should we leave that open tonight? There are storms and rain forecast for the night.

I have one more question if you don't mind. We are leaving on vacation next Friday for about 9 days. I don't have a reliable person to add chlorine for us. Should I just use the stick chlorine in the chlorinator during that time?

 

[chem geek]

If the storm is likely to put a lot of junk (leaves, etc.) in the pool, you can close the cover. If it's just rain, then leave it open. Not a big deal if you just close it for the night and then reopen it the next day.

For your vacation, yes you can use a bunch of Trichlor tabs or sticks in a floating feeder (or inline chlorinator). Just make sure it doesn't "park" itself in one place near the edge of the pool or else any metal and plaster in that area can get harmed (this is from personal experience). Since your CYA is low anyway, using the pucks/sticks for a short time won't add that much to CYA.

Richard

 

[jmlodin]

I just wanted to follow up with today's results and make sure I am on the right track. Last night at 7:00 the FC was 14. Didn't get the pool opened until 1:00 today and the FC is now only 6 and CC is still 1. It is about 35 degrees outside with rain. I think the thing to do is shock again to get FC back up until the CC goes down to .5 or less. Would the CC 1 be what is still bringing the FC down overnight?

 

[chem geek]

It sounds to me like you've got other substances that the chlorine is oxidizing such as algae that isn't quite visible or perhaps bacteria remnants. Remember that the CYA that gets broken down to produce ammonia which is a nitrogen food source for the bacteria (that's why they break it down) while this ammonia can also be a nitrogen food source for algae (they also use nitrates). At this stage, the CC will be low but may or may not get to zero until you've gotten rid of all the bacteria and algae -- even then, it's possible to have some remaining CC though direct sunlight can help get rid of that when you get to the end of this process (i.e. when FC holds overnight). You also mentioned that when you closed the pool it was "barely clear" so unless it's really clear now, you've still probably got a lot of dead algae in the water. Follow the Defeating Algae procedure including regular brushing, continuous pumping/filtering, and frequent cleaning/backwashing of the filter.

I assume that you didn't have sun in the morning and that you've got some CYA in the water so that the loss in FC isn't due to breakdown from sunlight. I'd bring the FC back up and keep it up until you don't see losses overnight. Unfortunately, it does seem like you've taken care of the "easy" part of getting rid of the excess ammonia, but now need to deal with the "harder" part of getting rid of bacteria and algae that have consumed some of that ammonia. I hope it's not the entire rest of the initial CYA since that would be another 100 ppm FC (cumulatively added, of course) to go.

Hang in there...Pool Owner Patience (POP). This just emphasizes why one should try and maintain chlorine levels in their pool over the winter when possible or otherwise treat it with strong anti-bacterial and anti-algae products (I know that the pool store last year didn't take care of your pool's high CYA problem which likely led to algae growth with too low an FC). I'm so sorry you are having to go through this, but at least you're likely never have to go through it again.

Richard

 

[jmlodin]

I continued to shock yesterday and last night at 7:30 the FC was 14.5 and CC was 1. I checked this morning at 11:00 (pool has been covered) and the FC is 10 and the CC is finally .5. Do I continue to shock since the FC didn't hold overnight? When you say hold do you mean it can't go down at all? Thanks for your continued guidance. BTW, the water looks good now.