Lego, made of ABS, Acrylonitrile butadiene styrene. Yes, @Brew12, you can have Lego in your reef tank.

This is a royalty-free image from by MW from Pixabay.

Welcome to Part 2 of Plastic for the Reef Aquarium. In Part 1, we covered some background on plastic, why plastic is of interest to reef aquarists, and we talked about plastic in general terms. Now we'll get a little more specific.

Unfortunately, most of the research that I've read about plastic does not test plastic specifically with saltwater. Plastic is typically tested with tap water or RO/DI water. So, we have to rely on information from chemistry experts like our own Dr. Randy Holmes-Farley, experience from reef aquarists, and common sense.

An unusual "drop-off" acrylic tank.

Photo is from the Reef2Reef archives and courtesy of @vetteguy53081, ©2019, All Rights Reserved.

I'm going to mention below some potential problems. However, I don't want to or intend to alarm anyone. I don't necessarily believe that these potential problems are serious and mean that you shouldn't use certain types of plastic.

But I would be remiss as a writer if I didn't at least mention what I've found in my research. I want to remind everyone that with most chemicals or additives, the dose makes the poison, and even plain RO/DI water is deadly if you're drowning in it. I'm not being flip.

Other things to consider are whether some research even applies to reef aquarists at all. When research is using water, it's often chlorinated water. The water we use has had the chlorine removed. So, do those results apply to reef aquarists? I don't know.

On the other hand saltwater is typically a lot more corrosive than plain water. Anyone live near the ocean? So, maybe research results would be more serious when using saltwater. Until someone actually does experiments using saltwater, we just don't know.

Also, anything that might leach out of plastic is possibly/probably made worse by heat and/or light. Reef tanks are usually kept warm and under bright lights. Just want to throw that out there.

And reef aquarists don't generally test water for the compounds that plastic could be adding. But then again, maybe the amounts of chemicals leached into the water--if any--are so small that they don't matter.

I mention all these points of discussion to underline that drawing conclusions here is no easy task. And if I leave you with more questions than answers, I apologize in advance.

So, here's a little table that I made for you, and then we'll look at the plastics I've mentioned one by one. I haven't mentioned every plastic known to man, just the ones that you're most likely to run into or use.

Screen Shot 2019-04-20 at 2.54.10 PM.png

Table courtesy of @Seawitch, ©2019, All Rights Reserved.

*Epoxies containing bisphenol-F instead of bisphenol-A are more chemically resistant when fully cured.

**I did not list all of the potential problems, just a few that stood out to me. See Reference (18).

Before we look at these plastics individually, I’d like to make the point that lots of plastics “offgas” or “outgas” some nasty things, especially when they’re new. What they are offgassing is volatile organic compounds or VOC’s, which are not good for us, and I dare say probably not good for our livestock. I found several references to “if you can smell it, then exhaust it,” meaning if it smells, then air it out. You can speed up offgassing by putting new plastic outside in the sun for a few days (or weeks) before use.

PVC is particularly notorious for this—as in have you ever walked into a room with a brand new vinyl floor?

So, overall, plastics are pretty safe for the reef, and I'll quote from Dr. Randy Holmes-Farley in one thread, where he says, "FWIW, there are very few commercially available plastics that are any concern in a reef (very likely none, but some may not be structurally suitable or stable long term in certain applications). The concern can be what a particular manufacturer might choose to put into the plastic as a filler, antimicrobial agent, uv protectant, antioxidant, etc." (23)

In my table above, I listed the plastics in alphabetical order, so I'll address them here in the same way.

Another way to look at plastics--by recycling classification.
plasticSS2019-04-18 at 1.02.30 PM.png

Screenshot courtesy of @Seawitch. Photo comes from a UK government pdf (30). ©2019, All Rights Reserved.

ABS: Acrylonitrile butadiene styrene

ABS is pretty popular for a lot of reasons. It's a thermoplastic plastic meaning it can be heated and melted down and reformed easily. It's easy to machine, and easy to recycle, for starters. It has a fairly low melting point making it popular with 3D printing. It's pretty resistant to both impact and corrosion. Its claim to fame is LEGO.

Now you wouldn't want to be breathing ABS vapors if you were manufacturing it or drilling it, but unless you turn up your aquarium temperature to 400C, then it seems to be among the safest of the plastics for reef livestock. In one of the Reef2Reef threads I referenced at the bottom, Dr. Randy Holmes-Farley said he had an ABS refugium for many years.

EP: Polyepoxide or Epoxy Resin

Seems pretty safe. Reef aquarists have been using it for years to coat things that they don't want to leach into the water--like coating pieces of driftwood so tannin doesn't leach from the wood. The key to using an epoxy resin is to let it set and cure. This is the same stuff that can be used on bar counters. It's hard, tough, and resistant to everything. Note that it stinks with a crash while curing.

It does appear that some epoxies can leach BPA. But not all epoxies are manufactured with BPA, so not all would or could leach it into the water column. And there's some research saying that BPA isn't as bad as once thought. (26) One thing is clear. If epoxy is going to leach BPA it leaches more of it when the water and plastic are heated.

HDPE: High-density polyethylene

Seems pretty safe. As long as you're dealing with the finished product and not the manufacture of it, then it's a tough, very resistant plastic. It's usually BPA-free when it's made, but I did find a paper that says it can leach some different esters, ketones, some hydrocarbons, and some vinyl compounds. (18)

I use HDPE gas cans (new of course) to carry water.

PC: Polycarbonate

Polycarbonate is typically used in sheets like to cover an aquarium. It can leach BPA, although there is such a thing as BPA-free polycarbonate. Polycarbonate has a lot of good qualities which I mentioned in Part 1, but it's a lot more expensive than acrylic, so I'm not sure it's worth it. It scratches very easily unless it's coated with some kind of resin to resist abrasion, but what that coating is, is not clear.

In response to Part 1 of this article, @Diznaster mentioned that aquarists should also consider the water absorption properties of plastics. @Diznaster said that a polycarbonate lid to a reef aquarium will often bow up over time due to the absorption of water and showed us this diagram below.
r2rMoisture Absorption.jpg

Diagram courtesy of @Diznaster, ©2019, All Rights Reserved.

I would like to add a couple of points to that discussion. Yes, polycarbonate does absorb some water. However, there may be some other things at play here. Polycarbonate is considered an amorphous plastic that is not married to the shape it comes in. Furthermore, in this case, the polycarbonate endures heat and the corrosive affects of saltwater from the underside and heat and light from the top side. So, I would venture to guess that a lid like this receives assault from both sides and water absorption may not be the only thing influencing the bend. I don't know.

I looked it up, and PC (under heat) has a water absorption factor of 0.10 to 0.20 and PMMA (acrylic), another amorphous plastic has (under heat) a water absorption factor of 0.20-0.40. (28) So, that makes me wonder if acrylic would bend worse if it's more inclined to absorb water. However, we know that PC is more "bend-y" and you can even cold-bend PC.

I'm going to stop here for today. Tomorrow or Monday, we'll cover the rest of the plastics in the table, and have our discussion and conclusions. Happy Easter.

































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Author Profile: Cynthia White

Cynthia received her BA in English from NYU a long long time ago. She has been a freelance writer and editor for over 20 years. In 2018, she won the President's Award from the Professional Writers Association of Canada. Now she is a writer and editor on staff at R2R, where her forum nickname is @Seawitch. She lives on Vancouver Island with her husband, three special-needs dogs, and three saltwater aquariums being set up.