SLAM levels dangerous to wildlife?


Active member
Aug 16, 2015
Bryan, Texas
I need to slam our pool to get rid of some stubborn algae, but was worried about the effects of high levels of chlorine on the local wildlife. We have a number of squirrels, possums and other critters which regularly drop by in the 100 degree heat to take a drink, and I was worried about any harm that may come to them drinking water that has been raised to shock levels.


Platinum Supporter
TFP Guide
Jul 17, 2015
I'm also not sure, so I set off to do a little research on the question, and found that if Borates are in the water the water is a lot more potentially toxic than if it is merely chlorine. Here is the article that talks about that.

I could be 100% off base in my assumption, and if so I apologize and hopefully someone will correct me if I'm wrong.

By combining what I've learned here at TFP, with my medical degree knowledge here are my thoughts. With everything above being said, and knowing the high FC levels may not be potentially harmful/fatal to the wildlife/pets if consumed in small amounts. Like with anything, they can always consume too much of a good thing, including plan ole tap water which can also harm/kill a person/animal if too much is consumed at any given time.

Then you have to still ask yourself this question: How much is too much? A 120 lb deer may be able to consume 2 cups of high FC water in a single setting without any side effects at all, yet Mr. Opossum comes in, and drinks himself 1 cup of high FC water twice in the same day then becomes ill from the amount.

IMO since we can not really determine how much is too much, nor force them to limit their daily intake I would suggest keeping the pool covered the entire during the SLAM process, and sit the Wildlife a Plastic Kiddy Pool off to the side refilling it daily with fresh low chlorine tap water. That way you can get your Slam done correctly, and still safely water the Wild animals who have come to rely upon you for their daily drinking water.

LOL I know this didn't exactly answer your question, but IMO it is always better to be safe than sorry. I'm really curious to read all the other comments that arise from this post. Have a nice night?


TFP Expert
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LifeTime Supporter
Moderator Emeritus
Aug 10, 2012
FL panhandle
I definitely killed more frogs when slamming. Borax doesn't seem to impact wildlife other than I have less bugs in the water. But, not more dead bugs. I didn't notice anything abnormal with squirrels, dogs, etc during the slam.


LifeTime Supporter
TFP Guide
May 14, 2015
Cartersville Ga
oops. sorry pooldv

Not sure if it's relevant, but I know frogs and toads don't fair to well. Snakes not so good either. But all those are found in the water so probably not indicative of the experience of other visitors.

Divin Dave

TFP Expert
LifeTime Supporter
Oct 2, 2013
Longview, Texas
I cant answer the question scientifically, but I doubt it. Most wildlife have a built in danger sensor, but then Im not a wildlife biologist either.

The question that pops into my mind, is how you might intend to kill all of the algae without using large amounts of chlorine. Be it by liquid chlorine and slamming or by using powdered pool shock, etc. The net effect of chlorine is that it all turns into hydrochlorous acid at the end of the day.

Of course I supposed draining, chlorine washing and refilling is an option, but would still need shock levels of chlorine for at least some amount of time.

Anyways, I like the idea of a kiddy pool for the wildlife.


Mod Squad
TFP Expert
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In The Industry
Apr 1, 2007
Sebring, Florida
I would suggest keeping the pool covered the entire during the SLAM process,
That's not a good plan. All pools want to "breathe" and a SLAMmed pool particularly needs to breathe. Having access to UV rays and (to a small extent) even fresh air is VERY important to the SLAM process and should not be overlooked. I suggest you keep your pool uncovered during the entire SLAM.

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
For drinking the water, what is relevant is the FC level since that is the capacity or reservoir of chlorine. The FC/CYA level isn't as relevant since the effects are not rate-based as much as they are quantity-based since chlorine reacts fairly quickly when ingested. For mammals, even SLAM levels should not be harmful. Rat studies had a difficult time even determining a No Observed Adverse Effect Level (NOAEL). See the EPA Integrated Risk Information System (IRIS) entry for chlorine where rats fed 275 ppm chlorine for up to 104 weeks showed essentially no effects except that at this highest dose the rats drank somewhat less water after one year. The EPA uses a Margin of Exposure (MOE) or uncertainty factor of 100 (10 for inter-species variation and 10 for intra-species variation) so is how they get to 0.144 mg/kg/day as a limit that informed them to get to 4 ppm FC as a drinking water limit for 2 liters per day for an 55 kg (122 pound) person.

So you should not worry about squirrels, possums, deer, or other mammals with regard to chlorine consumption. Smaller mammals drink less and what is relevant is how much they drink relative to their body weight, but for chlorine it would take such a high amount that it isn't of concern.

On the other hand, chlorine is much more toxic to aquatic wildlife, especially to fish. See Toxicity of Combined Chlorine Residuals to Freshwater Fish, Chlorine-induced Mortality in Fish, and Effects of Residual Chlorine on Aquatic Life. Here the issue is the active chlorine level (related to the FC/CYA ratio) because it is the rate of chlorine reaction with sensitive body parts that is relevant. Fish gills are particularly sensitive and this may be from oxidation of the ferrous iron (Fe2+) in hemoglobin to become ferric iron (Fe3+) in methemoglobin where the latter cannot bind oxygen so the fish die of anoxia. Even regular chlorine levels at the minimum FC/CYA ratio would be harmful to most small fish, at least giving them distress (it's equivalent to 0.06 ppm FC with no CYA). SLAM levels (0.6 ppm FC with no CYA) would be toxic to virtually all small fish (i.e. those one would find in ponds).

As for frogs, they are probably in between the fish and the mammals. Tadpoles use gills so would be affected by chlorine more like fish. Frogs lose their gills and breathe through lungs so are affected by chlorine more like mammals. The thread Please Help! Frogs in the Pool! indicates that frogs are not affected by regular FC/CYA levels. The posts in this thread seem to indicate that SLAM levels are toxic to more frogs. Some areas in frog skin are permeable and if chlorine enters a frog's bloodstream then the same effects of anoxia to fish could happen to frogs. This is true in general for amphibians that allow oxygen to enter through their skin into blood vessels near the surface of the skin. Hypochlorous acid looks a lot like water so if the skin is permeable to water it will likely let chlorine pass through.


Well-known member
Apr 29, 2015
Sarasota, FL
I think the reason more frogs are killed during a SLAM is because the pump is running 24/7, particularly at night. I have seen many frogs in my pool at night that are able to climb out the side of the pool since the water is calm, but when the pump is running they cant get out and eventually end up in the skimmer basket. I don't think the elevated FC has anything to do with it

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