Could this be algae or dirt/pollen?

[joliecharlie]

Let your chlorine drop to "normal" levels but keep it as suggested at around 6 ppm FC or so minimum (at your current 40-50 ppm CYA level) and see if this stuff returns. If it does, then you can try shocking to higher levels (20-25 ppm) as I mentioned in my earlier post.

Richard[/QUOTE]

Hi Richard,
Just checked the chlorine after full day of sun and 80-85 degree weather here in NC.
FC has dropped by 5ppm since this morning. (Remember it held stable overnight at 15ppm)

Is it normal to lose that much chlorine in a day?

[chem geek]

That does seem a bit high for a drop. Losing half of the chlorine over a day is more typical -- so 15 ppm to 7-8 ppm would be more "normal". Then again, I could be wrong about those half-life numbers. They seem to be correct for most pools, but there's no arguing whatever it is that you are seeing in your pool. It's also not like you are in south Florida or the middle of summer. Maybe there is in fact some algae in your pool and it is growing more during the day and consuming more chlorine, but typically if it holds overnight then this means the algae is gone. Sorry I don't have a good answer for you.

Richard

[chem geek]

OK, I've been thinking more about this and I believe you do still have a chlorine demand with this (presumed) algae. It's probably a demand of 1 ppm per 8 hours or maybe a little more. That would "seem" like the chlorine holds overnight, but if you lose half from the sun 15-->7.5 and then another 2 or more from chlorine demand from the algae, then that would get you to 5.

So, I would suggest really hitting this algae with a lot of chlorine. Start with 30 ppm FC in the morning. If you are able to stick around and add more chlorine during mid-day, do that, otherwise add more when you get home at night. Keep this up until 1) there is no more visible red dust and 2) the chlorine holds solidly overnight (virtually no drop at all) and holds more during the day so it drops no more than half.

If that works, then the question becomes how to keep this algae away ongoing. Though you could maintain a minimum of 6 ppm FC at 45 ppm CYA (or 8-9 ppm FC at 60 ppm CYA) which is what some others have found is required to keep away mustard/yellow algae, there is another way that might let you keep lower chlorine levels. See this thread for the use of 30-50 ppm Borates in the pool which act as an algaecide (as well as an additional pH buffer). The problem is that we don't know if this is a good algaecide specifically against mustard/yellow algae though it does inhibit a variety of different algae. Anyway, I just wanted to give you a long-term option that might help since this is a repeated problem for your pool that would require higher chlorine levels to keep away (even at 30 ppm CYA, you might have to keep a minimum of 5 ppm FC to keep away mustard/yellow algae instead of the normal 3.5 ppm FC mid-point recommendation).

Richard

[joliecharlie]

Hi Richard,

You are so kind to help me. I may have been unclear in the previous post about the loss I experienced. I started the day Sunday at 15ppm (it held overnight Saturday) and ended the day Sunday with 10ppm.. a 5ppm loss.

I added Bleach last night to bring it to 18ppm ( I also put one trichlor puck in the skimmer)and checked this afternoon. The chlorine is 14.5ppm. It was not as hot today, but sunny almost all day. I added another 96oz of 6% bleach (usually gives me 3ppm rise) a little bit ago. I know when the CYA was about 60, I did not have as big a drop daily. You did a survey last summer and asked me for my numbers ( I don't remember them now)

I am nearly positive this is some sort of dirt/pollen. It brushes away very easily, just the momentum of the water will disturb it. I cannot find anything on the walls or ladder. I have run my fingers under the ladder step and found nothing.

I am reluctant to add more stuff to my pool because one of my 4 legged children drinks out of it! I hate to even use algaecide, so I am not too sure about the borate....although I realize if we had city water it would be the same thing or close to it.


Mary Beth

[chem geek]

The survey is at this thread (it was actually leejp that asked the question). Unfortunately, what was not asked for the table was the FC level when the additional chlorine was added. This is important because the absolute amount of chlorine that is lost through sunlight is proportional to the amount of free chlorine (FC) in the pool. If you have twice the FC level, you will lose twice as much chlorine.

Sorry I misinterpreted your numbers. Going from 15 ppm to 10 ppm (a 33% loss) is quite normal as is 18 ppm to 14.5 ppm (a 20% loss).

I hope you are right that it is just dirt or pollen. That certainly a lot easier to deal with!

As for your dog (I assume that's the 4-legged creature), the EPA reference limit for chlorine of 0.1 mg/kg/day so for a 10 kg (22 pound) dog that comes to a limit of 1.0 mg/day so at 15 ppm (mg/l) FC that is 67 ml or about 2.3 fluid ounces per day. This is the limit where there were no adverse side effects whatsoever -- it's not a limit for chronic toxicity which is much, much higher (14.4 mg/kg/day) -- and is worst when inhaled rather than drank. The fact that there is CYA in the pool probably doesn't matter at all since the chlorine will get released from the CYA as it is used in the body.

For boron (borates), in dogs at 0.44 mg/kg/day there was noticeable decrease in spleen to body weight in males, but that was the only effect and is the lowest dose with any known effect. Boron in humans actually has potential nutritional importance, at a requirement rate of around 0.75 kg/day with normal safe amounts of around 1-13 mg/day (this translates to around 0.015-0.2 mg/kg/day). So using the 0.44 mg/kg/day as a limit, then for a 10 kg dog this comes to a limit of 4.4 mg/day so at 50 ppm Borates (which is actually measured as ppm Boron by convention) that is 88 ml or 3.0 fluid ounces per day.

So the bottom line is that both the high chlorine level of 15 ppm and a 50 ppm Borates level are both a problem for dogs drinking regularly from a pool if they do that every day drinking, say, a cup or more every day and the technical limit below which there are no symptoms would be less than half a cup every day. I again want to stress that the amounts are for the lowest limits below which there are no symptoms or measured body changes (even after years of exposure at these levels).

City water, by the way, probably doesn't have any chlorine in it at all since most municipalities have switched to using monochloramine as the residual instead, mostly due to newer strict requirements at reducing the amount of disinfection by-products in drinking water. Also, if there was residual chlorine in the water, it is likely to be at very low levels less than 1 ppm FC. In fact, you can easily measure the FC level of your drinking water and if monochloramine is used instead, then your FC will measure near zero, but your Total Chlorine (TC) will measure high (since monochloramine measures as combined chlorine). There are usually no Borates (or Boron in any form) in drinking water.

Richard

[dawndenise]

So the bottom line is that both the high chlorine level of 15 ppm and a 50 ppm Borates level are both a problem for dogs drinking regularly from a pool if they do that every day drinking, say, a cup or more every day and the technical limit below which there are no symptoms would be less than half a cup every day.
Richard

Thank you for posting that info. I'd been concerned about adding borates to my pool for exactly that reason, having remembered something I read a long time ago about boric acid being toxic to canines. I started to do some searching and was having some difficulty slogging through the chemistry - although it appeared that borates, and their chemical relatives, are NOT good for dogs at the level being considered for the pool. I had hoped to post a question about borates and canines after I could better understand the articles I was finding. Thankfully, I don't have to do that now!

I have a swimming pool fool (canine) that believes we constructed this wonderful outdoor water bowl specifically for her, so I'm certain she drinks more than a cup of water a day plus there's the amount that gets into her mouth as she splashes about and swims. She's approximately 55-60 pounds.

I guess we'll skip the borates and hope we don't have a repeat of the dreaded yellow/mustard algae this fall.

Thanks again for that info.

[chem geek]

Sandy,

I don't want to needlessly worry you, but the point I was making was that the chlorine in the pool was also a problem, not just the Borates. Though I used the example of a high chlorine level of 15 ppm, a level of 5 ppm would also be a problem since the limit of no symptoms would be about 12 fluid ounces or a cup and a half per day for 22 pounds so for your dog it would be about 2.5 times that amount (so about 30 fluid ounces or 4 cups). And yes, your dog drinking more than a cup of water per day would exceed the "no symptoms" limit for Borates, but would also be closer to the "no symptoms" limit for chlorine. The Borates limit of "no symptoms" for your dog is around 8 fluid ounces or one cup per day.

Again, these are "no symptoms" limits, not limits for toxicity. Nevertheless, to the extent that you can try and restrain your dog from drinking a lot every single day from your pool, that would be better. Perhaps having a water dish nearby with an occasional treat present might wean her away, at least some of the time.

So, bottom line, you are right and probably safest to avoid the Borates if you can't keep your dog from drinking the pool water regularly.

Richard