# How should I kill moss in an outdoor fountain. **URL:** \ **Category:** Factual Questions\ **Created:** [March 21, 2006, 8:07pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332 "2006-03-21T20:07:28Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![Foybal](https://avatars.discourse-cdn.com/v4/letter/f/fbc32d/32.png) [@Foybal](https://boards.straightdope.com/u/Foybal)\ **Post date:** [March 21, 2006, 8:07pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/1 "2006-03-21T20:07:28Z")
I’ve got a large fountain and the moss is gross. I drained it once and brushed it down with simple bleach, which lasted all of one month. Anything else I can do? (That won’t kill birds and children who splash there) ---
**Author:** ![Burrido](https://avatars.discourse-cdn.com/v4/letter/b/3be4f8/32.png) [@Burrido](https://boards.straightdope.com/u/Burrido)\ **Post date:** [March 21, 2006, 8:22pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/2 "2006-03-21T20:22:10Z")
There’s chemical cleaners made from biodegradable fatty acids. At work we use some kind of acidic cleaner. I’ll grab the name tomorrow. It’s decent but probably not safe for birds or kids. I splashed myself with a bit and it burned a little. Our fountains are huge and the algae/moss is a much bigger problem so you may be able to get away with the chemical ones. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [March 21, 2006, 10:51pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/3 "2006-03-21T22:51:42Z")
Many people with horses have large water tanks for them to drink from. It’s common to keep some goldfish in the tank to eat up the moss. You could try that. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [March 21, 2006, 10:58pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/4 "2006-03-21T22:58:01Z")
Are we talking about actual moss here, or algae? ---
**Author:** ![Rhubarb](https://avatars.discourse-cdn.com/v4/letter/r/59ef9b/32.png) [@Rhubarb](https://boards.straightdope.com/u/Rhubarb)\ **Post date:** [March 21, 2006, 11:11pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/5 "2006-03-21T23:11:55Z")
I use a small piece of a swimming pool chlorine tablet in mine. This not only kills the algae, it discourages birds from crapping in the fountain. My dog still drinks out of it and has shown no ill effects so far. It does tend to etch the concrete in the fountain, so I use it sparingly. I assume that bromine tablets would work equally well, but I can’t speak as to their toxicity to birds, dogs or children If you don’t want to go the chemical route you can try the biological approach suggested by **T-Bonham** , but you may kill a few goldfish when the water level gets low, or you can drain and brush it every few weeks. Or just look at your fountain as an auxiliary oxygen generator and learn to love the algae. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [March 21, 2006, 11:26pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/6 "2006-03-21T23:26:13Z")
Well, of course, chlorine and bromine are poisons. They kill living things. The amount you use determines what dies. You’ll wind up doing some type of balancing act in the long run because in order to kill the algae you’re going to have to poison it with something, and chances are what you use will be toxic to other living things, e.g. birds and other visitors to the site. Any chance you can scrub the algae away? Any chance you can tolerate its presence? ---
**Author:** ![Contrapuntal](https://avatars.discourse-cdn.com/v4/letter/c/e274bd/32.png) [@Contrapuntal](https://boards.straightdope.com/u/Contrapuntal)\ **Post date:** [March 21, 2006, 11:31pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/7 "2006-03-21T23:31:00Z")
> [@Rhubarb](#): > > My dog still drinks out of it and has shown no ill effects so far. It does tend to etch the concrete in the fountain, so I use it sparingly. So your dog drinks a solution that etches concrete? Can I persuade you to take a sample to your vet so it can be examined? “No ill effects so far” could easily be “terrible bad shit down the road.” ---
**Author:** ![drachillix](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@drachillix](https://boards.straightdope.com/u/drachillix)\ **Post date:** [March 21, 2006, 11:45pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/8 "2006-03-21T23:45:46Z")
> [@Foybal](#): > > I’ve got a large fountain and the moss is gross. > I drained it once and brushed it down with simple bleach, which lasted all of one month. > Anything else I can do? (That won’t kill birds and children who splash there) IANA botanist but I worked in an amusement park with alot of water features. The solution chlorine or UV sterilization. High power aquarium UV sterilizers should keep your algae in check, if not a handful of small freshwater snails should keep it down as well. Look around in pet stores sometimes you can find plants like anacharis that are covered with the things. To the store they are often unwanted pests. If you can find tiny ones they should thrive and multiply like weeds. Birds and critters will of course skim off a few but if its a decent size fountain they will never get them all. Goldfish arent the greatest algae eaters , maybe a plecostomus or five might make a nice addition as well. Good luck ---
**Author:** ![Eleusis](https://avatars.discourse-cdn.com/v4/letter/e/f4b2a3/32.png) [@Eleusis](https://boards.straightdope.com/u/Eleusis)\ **Post date:** [March 21, 2006, 11:49pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/9 "2006-03-21T23:49:52Z")
I’d look at stuff for fish tanks… that can’t be too toxic [http://www.drsfostersmith.com/product/NavResults.cfm?N=2004+113000](http://www.drsfostersmith.com/product/NavResults.cfm?N=2004+113000) ---
**Author:** ![WhyNot](https://avatars.discourse-cdn.com/v4/letter/w/c77e96/32.png) [@WhyNot](https://boards.straightdope.com/u/WhyNot)\ **Post date:** [March 22, 2006, 12:12am UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/10 "2006-03-22T00:12:19Z")
Have you tried barley bales or barley balls? They work well in my pond, they’re completely non-toxic and cheap, as well. ---
**Author:** ![Foybal](https://avatars.discourse-cdn.com/v4/letter/f/fbc32d/32.png) [@Foybal](https://boards.straightdope.com/u/Foybal)\ **Post date:** [March 22, 2006, 3:00pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/11 "2006-03-22T15:00:17Z")
> [@Eleusis](#): > > I’d look at stuff for fish tanks… that can’t be too toxic > > [Pet Supplies, Pet Food, and Pet Products | Petco](http://www.drsfostersmith.com/product/NavResults.cfm?N=2004+113000) Thanks. Those products look about right. And they don’t kill the fish, so I’d guess they won’t hurt birds. Those [Barley Balls](http://www.gardeners.com/on/demandware.store/Sites-Gardeners-Site/default/ViewProductDetail-SellPage?OfferID=14163&SC=) sound nice for a pond, but they are too big fo my fountains, which are just 20’ wide. ---
**Author:** ![Seven](https://avatars.discourse-cdn.com/v4/letter/s/3d9bf3/32.png) [@Seven](https://boards.straightdope.com/u/Seven)\ **Post date:** [March 22, 2006, 3:18pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/12 "2006-03-22T15:18:13Z")
I wonder if just pushing the Ph up would do the trick? Try adding a bunch of baking soda to the water - like a whole carton. ---
**Author:** ![Amazon\_Floozy\_Goddess](https://avatars.discourse-cdn.com/v4/letter/a/779978/32.png) [@Amazon\_Floozy\_Goddess](https://boards.straightdope.com/u/Amazon_Floozy_Goddess)\ **Post date:** [March 22, 2006, 4:41pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/13 "2006-03-22T16:41:53Z")
I use a product called Algae Destroyer. A small tablet treats several liters of water. It’s non-toxic and I’ve used it several times with good results (fish were fine also). ---
**Author:** ![ivn1188](https://avatars.discourse-cdn.com/v4/letter/i/e480ec/32.png) [@ivn1188](https://boards.straightdope.com/u/ivn1188)\ **Post date:** [September 6, 2010, 5:25pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/14 "2010-09-06T17:25:42Z")
> [@Contrapuntal](#): > > [QUOTE=Rhubarb] > My dog still drinks out of it and has shown no ill effects so far. It does tend to etch the concrete in the fountain, so I use it sparingly. So your dog drinks a solution that etches concrete? Can I persuade you to take a sample to your vet so it can be examined? “No ill effects so far” could easily be “terrible bad shit down the road.” [/QUOTE] This is silly. Pure water will etch and discolor concrete, and kills a lot more people each year than chlorine does. If the water was dangerous due to chlorine, the dog would be dead, or the dog would not drink the water because it would smell truly awful. It’s not like the dog is going to get long term chlorine poisoning – the symptoms of poisoning are not exactly subtle. Wasting money taking a water sample to a vet is a laughable waste of time and money for everyone, as well as being an exercise in fearful ignorance. Furthermore, I’m pretty sure he means that the tablet itself can mark up the concrete, not the water. ---
**Author:** ![Jenaroph](https://avatars.discourse-cdn.com/v4/letter/j/e8c25b/32.png) [@Jenaroph](https://boards.straightdope.com/u/Jenaroph)\ **Post date:** [September 6, 2010, 6:20pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/15 "2010-09-06T18:20:35Z")
> [@ivn1188](#): > > > [@Contrapuntal](#): > > > > So your dog drinks a solution that etches concrete? Can I persuade you to take a sample to your vet so it can be examined? “No ill effects so far” could easily be “terrible bad shit down the road.” > > This is silly. Pure water will etch and discolor concrete, and kills a lot more people each year than chlorine does. If the water was dangerous due to chlorine, the dog would be dead, or the dog would not drink the water because it would smell truly awful. It’s not like the dog is going to get long term chlorine poisoning – the symptoms of poisoning are not exactly subtle. Wasting money taking a water sample to a vet is a laughable waste of time and money for everyone, as well as being an exercise in fearful ignorance. > > Furthermore, I’m pretty sure he means that the tablet itself can mark up the concrete, not the water. Dog might be dead now anyway. It’s been 4 1/2 years… ---
**Author:** ![Contrapuntal](https://avatars.discourse-cdn.com/v4/letter/c/e274bd/32.png) [@Contrapuntal](https://boards.straightdope.com/u/Contrapuntal)\ **Post date:** [September 7, 2010, 2:29pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/16 "2010-09-07T14:29:22Z")
> [@ivn1188](#): > > If the water was dangerous due to chlorine, the dog would be dead, or the dog would not drink the water because it would smell truly awful. Because we all know a dog will \*never \*ingest anything dangerous, right? ---
**Author:** ![YogSothoth](https://avatars.discourse-cdn.com/v4/letter/y/8edcca/32.png) [@YogSothoth](https://boards.straightdope.com/u/YogSothoth)\ **Post date:** [September 7, 2010, 10:06pm UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/17 "2010-09-07T22:06:20Z")
Have you tried rolling it around? 😃 ---
**Author:** ![ivn1188](https://avatars.discourse-cdn.com/v4/letter/i/e480ec/32.png) [@ivn1188](https://boards.straightdope.com/u/ivn1188)\ **Post date:** [September 8, 2010, 2:14am UTC](https://boards.straightdope.com/t/how-should-i-kill-moss-in-an-outdoor-fountain/349332/18 "2010-09-08T02:14:37Z")
> [@Contrapuntal](#): > > > [@ivn1188](#): > > > > If the water was dangerous due to chlorine, the dog would be dead, or the dog would not drink the water because it would smell truly awful. > > Because we all know a dog will \*never \*ingest anything dangerous, right? Well, that logic is irrefutable. Dogs sometimes eat poisonous substances, therefore dogs eat every poisonous substance. Without pointing out the obvious logical flaw here, let me just explain to you that water chlorinated to the point of toxicity will burn your mucous membranes, cause choking and coughing, sting your eyes, and probably burn your tongue, and will do the same to dogs. These effects tend to repel dogs, as illustrated by the efficacy of pepper spray.