EPDM - Fish Safe vs Roofing Liner

Companies I could find manufacturing fish safe EPDM liners.

Define "fish safe"

I read many posts on water garden forums about whether EPDM roof liner is safe for ponds or if fish safe liner should be used. What is always missing is any discussion about whether fish safe liner is safe. No one questions the manufacturer claims.

Certainly EPDM liner is reasonably safe. It's been used in ponds for many years and there's been relatively few claims of fish dying because of the liner. In one case I offer to pay for postage to get a sample of the killer liner so I could test it but the poster wouldn't agree. I personally think EPDM is a great liner. But there are few things in this world that are 100% safe so I won't go that far.

Manufacturer Claims

Firestone does not currently provide any information on why they consider their liners fish safe. Many years ago I did find a document on their web site that was about a page which said they made a pond, put in 6 goldfish and in 2 weeks the fish were still alive. That's the entire test.

Anjon touts they're "the only manufacturer to publish the fish safe certification of our EPDM liner on the Internet". And they do here. In 2000 Anjon hired Guardian Systems to perform the following test. Four Shubunkin goldfish in a 15 gal tank and a 2'x5' piece of EPDM for 2 weeks. All lived, so liner is deemed fish safe. Basically the same test as Firestone.

Manufacturer Warnings

I've never read on a roof liner manufacturer's web site any warning not to use the product in fish ponds. Zero. Certainly they know their product is being used in ponds. If they had any concern I assume their lawyers would have them cover themselves with a warning. At most they simply refer people to their pond products.

Prove the Myth False for Yourself

The answer to whether roof EPDM is safe or not is super easy to answer. Do the exact same test on whatever liner you want to use. You'd have the exact same fish safe certification given by manufacturers. Obviously hundreds or thousands of people have done this test by simply using roof EPDM liner in ponds and having fish live more than 2 weeks. Actually these tests are much more exhaustive test since these liners have been in use for many years, many conditions and using lots of fish, plants, instects and bacteria.

If one believes the manufacturer fish safe claims then they certainly should believe the more exhaustive tests on roof liner. Unfortunately that would only happen in a debate where facts mattered.

Anything worth saying is worth exaggerating

Retailers like to punch up the claims a little bit.

"Firestone Pondgard 45 mil EPDM liner is manufactured to be fish safe. That means that the ingredients used in making the liner are perfectly safe for your fish." Do take "perfectly safe" to mean 100% safe? I do. No proof is given. No guarantee is given either by the manufacturer or the retailer...only the claim is made.

"In the history of Firestone brand pond liner no fish has EVER been determined to have died from exposure to Pondgard liner." Wow, that's pretty safe. Of course I'm pretty sure in the history of ponds no one has ever had a dead fish tested to see if the liner caused the death. What would you even check?

"Roofing material is often made with harsh ingredients such as arsenic that can sicken or kill your fish." Wow! Yeah, arsenic, that stuff is bad. Arsenic is of course also used in the production of fish safe liner. There's also arsenic (2-10 ppb) in your drinking water, and in the water you're going to use to fill the pond. Using a dangerous chemical in a material doesn't automatically make that material dangerous. Chlorine is a primary ingreident in PVC pipe. The amount of chlorine used to make a short length of pipe would kill you in minutes if released in a room. Yet PVC is very safe. Chemistry vs scare tactics.

“TOXIC POND OF DEATH” OK, I get it. I must buy your liner...even though you don't provide a written guarantee. I use the retailer Graystone as an example only because they popped up first in Google. Many retailers use the same scare tactics and much worst.

I've never been able to find a manufacturer state they added an algaecide or fungicide to any plastic. Lot's of retailers love to say their fish safe liner "contains no algaecides...found in roofing EPDM". That quote was for the Firestone liner. If if you watch Firestone's video you see they tout the PondGuard product as "Algae and microbial resistant". Retailer claims of no algaecide in fish safe liners are just plain lies. And then we're suppose to believe is that algaecides in fish safe liners are safe and those in roof liner are not safe? Untrue because the same "algaecide" is used in both.

Most people seem to think something is added to the liner to make it resist algae and fungus. However regular glass is even more algae resistant than EPDM and no one thinks a chemical was added, or that it leeches something. For the most part when manufacturers say "algae resistant" they're just saying algae has a harder time growing on the material compared to other materials commonly used in the same application. The reason EPDM is algae resistant is because it's slick, just like glass. Algae certainly will grow on EPDM and glass where there's standing water. Certainly algae has no problem in EPDM lined water gardens.

Fire Retardants
Fire retardant doesn't mean toxic. Chlorine in PVC is what makes it fire resistant. Doesn't mean PVC leeches toxic chemicals. In EPDM it could be as simple as carbon. Manufacturers don't make it clear how or why they consider their material algae, fungus or fire resistant. However this stuff goes on roofs. Millions of roofs. With rain run off into our streams and lakes. It seems implausible to me that they would knowingly add any chemical that could leech out. There certainly could be some unknown interaction that in 20 years gets traced back to roofs, but that's true for anything, including fish safe liner.

Recycled Product
EPDM and HDPE I've seen that were food safe were white. Black almost always seem to not be FDA approved food safe. I think this is because non-white contains, or can contain, recycled material. The result is not white and so a dark color is added to even it out. Because every batch is unique it can't be called food safe. No reason to think these are not food safe...it's just that it makes no sense for the manufacturer to send every batch out for FDA approval. Food safe products are made with 100% virgin chemicals so they know every product is the same.

If you're concerned you can easily perform the standard fish safe test for yourself. Are your fish alive after 2 weeks?

Why exaggerate?

Why not exaggerate? Most pond myths come from retailers selling products as well as a few manufacturers. There has been zero downside to lying and using scare tactics to sell products. I've never read a single forum post suggesting that retailers posting obvious lies should be boycotted. Currently these myths are so widely believed it seems customers demand retailers make these claims or people will take their business elsewhere.

There is also a strong connection between many retailers and water garden forums. Mom and pop retailers are frequent forum posters even if not disclosed. Often considered experts because they've made lots of posts. Retailers also advertise on forums. I don't believe there's any conspiracy to defaud people...but there sure isn't any stampede to question myths either.

Is your fish safe liner actually roof liner?

I bought it from someone who said it was, so it must be. You know, the same people lying to me with scare tactics to get me to buy. No chance these completely "honest" people pull a little switch-a-roo and sent a cheaper roof liner? Nah, no way.

PondGuard supposedly does mark their liners, and I believe they probably do. But I personally have never found the mark on any fish safe liner. And I've never seen any mark on roof liner either, warning or otherwise. If you get an unmarked fish safe liner the retailer will say it just happen to be cut from a part of the roll with no marks. There is no way to distinguish between most roof and pond EPDM liners, even in a lab. Other than of course the word of the person selling the liner.

The peace of mind purchased in buying fish safe liner is dubious at best.


This myth was hot in the early days because fish safe liner was being sold was commonly 2 and 3 times more expensive than roof liner. As so many people have used roof liner in ponds and time has passed with no problems the toxic myth has lost most of its impact. So prices for fish safe liners have dropped. Roof liner can still be found being a little cheaper, but not much. And it's not uncommon in 2012 to find roof liner being more expensive than fish safe. So there's little reason to push the myth, but it remains. Now it's mostly a convenience issue, where it's easier to get roof liner vs fish safe.

But there are people still trying to find gullible people willing to believe scare tactics. Once found these marks probably won't do any comparison shopping and will pay 3 times as much for the same product found a few clicks away. These people are also goldmines for buying all kinds of other crap.

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