HDPE vs. Acrylic Sumps

It is our experience and opinion that high density polyethylene (HDPE) is a far superior material for aquarium sump use as compared to glass or acrylic. Below is an explanation of the various reasons.

  • HDPE tubs are one piece molds, not glued/welded which creates weak spots
  • HDPE Molded sumps have much stronger corner joints than glued/welded sumps
  • Baffles/glass lid recesses are molded in, not glued/welded
  • Molded HDPE tubs have smooth, rounded corners which are much easier to clean
  • Nothing sticks to HDPE-including algae
  • HDPE is highly resistant to chemicals and solvents

Molded vs Glued / Welded

One of the biggest advantages of our HDPE Seamless Sump® system is the fact that the tub designs are one piece molds rather than glued or welded parts. The one piece molded design has a lot of advantages which we will explain below.

Corners are the STRONGEST part of the tub, not the weakest

For most acrylic sumps are machined/fabricated and have glued or welded joints. This means the corner seams of the acrylic sumps are inherently the weakest part of the sump tub. This can be both because of the inevitable possibility of fabrication flaws, or because the adhesive/welding process creates a slightly more rigid and brittle joint than the rest of the structure making it weak and vulnerable to cracking over time. The OPPOSITE is true with a one piece molded HDPE tub.

To understand why the HDPE molded tubs have stronger corners, it is important to understand how they are manufactured. The manufacturing process used to create a one piece HDPE tub is a rotational molding process. This process consists of a metal tool that is machined to have the outer shape of the desired part that is designed using a 3D computer model. Plastic resin is added to the core of the tool and heated up as the tool starts spinning in all directions. Eventually you have molten HDPE in the middle of the mold/tool. As the mold rotates, the HDPE aquarium sump material slowly sticks and cools to the sides of the mold with centrifugal force and takes the shape of the desired part. The nature of this process means that a thick layer of material accumulates in the corners of the part as the tool is cooling because the material has a harder time flowing around the corners of the part as it is spinning that in the flat areas. This gives all of the corner joints a lot more material and strength and is a great advantage of this process.

Baffles and glass lid recesses are molded in, not glued in

You will notice that our unique patent pending Seamless Sump® Baffle Tub design is the only aquarium sump of its kind where the baffles are molded into the part rather than glued or welded in. This gives the baffle unmatched strength and integrity whereas in fabricated and also makes them easier to clean. You will also notice many structural ribs and indentations molded into the tubs that give increased strength and integrity to the flat areas. You will not see this in a glued/welded tub made out of flat sheet material.

Molded HDPE tubs have smooth, rounded edges and corners

You will also notice that all of the corners, inside and out, have smooth edges with large rounded radius. This is also a benefit of the rotational mold process. This makes sure that the tubs are easy to clean and you do not have difficult creases and glue / weld joints for algae and bacteria to fester.

Thick, Rounded Corners and Structural Recesses

Makes tubs extra strong, durable over time, and easy to clean. No seams to become brittle, crack, or LEAK!

HDPE Advantages

Nothing Sticks to HDPE

Another attribute to HDPE as a material of choice is the fact that nothing sticks to it. No glue, epoxy, paint, adhesive, will stick to the material. Although this can cause a problem for some manufacturing processes, it makes it a great material for this because that also means algae will not bond to it and it will be easy to clean. This also means rather than our aquarium sump tubs being fabricated out of glued or welded pieces, the best way to fabricate our Seamless Sump® products is to mold them.

Acrylic is Porous

As we explained in our pros and cons of glass vs acrylic section, acrylic is a much more porous material than HDPE. This means it absorbs the chemicals around it, algae will stick to it easier, and it becomes brittle and yellows over time. Because it is transparent in nature, it also does not age as well in the presence of UV light.

HDPE is Highly Resistant to Solvents and Chemicals

HDPE is often used for applications such as landfill liners, fuel storage containers, bottle caps, food containers (such as milk jugs) etc. because of these characteristics. As you can see below, HDPE is also the material of choice for many applications where caustic, harsh materials are present - such as ocean buoys and salt spreader hoppers. You simply will not see products like this being made out of acrylic or glass for a reason.

Ocean Buoy

Ocean Buoy

Salt Spreader

Salt Spreader

HDPE is Semi-Transparent - No "Nasty Tub" Syndrome

One of the most obvious visible difference you will see is that HDPE is a semi-transparent, sort of a "milk jug" color, whereas acrylic is typically clear. At first the clear acrylic might seem nice that you can see inside of your aquariums sump easily, however lets remember that the sump tub is where all of your debris and refuse ends up...this means in a very short amount of time, your nice clear acrylic sumps will look yellow, green, and a bit nasty. The semi-transparent HDPE aquarium sumps are clear enough for you to see the water levels in your tub, but not so clear where it looks unsightly when you open your cabinet doors. And remember, since NOTHING sticks to HDPE, it is much easier to clean.

First Nasty
Second Nasty
Third Nasty

If HDPE is So Good, Why are Most Sumps Made of Acrylic?

The main reason most aquarium sump systems are made of acrylic is because acrylic sumps are easier to fabricate. Anyone with a table saw and a can of glue or a welder can make an acrylic sump. However, the end result is not so desirable. They are typically prone to flaws, blemishes, and weaknesses. Because HDPE has to be molded, not glued, it requires a unique design with a significant investment in engineering and tooling. With our vast experience with servicing our own aquariums (SerenityUSA.com) we spent a lot of time and resources creating that unique design and went the extra mile with our tooling to create the highest quality, most comprehensive elegant filter system on the market.

Why is Glass the Best Choice for Aquariums but HDPE is the Best Choice for Sumps?

As we explain in our Glass vs Acrylic section of this web site, we strongly believe that glass is a better material for aquarium use than acrylic. However, when it comes to aquarium sump use we feel that HDPE is better than both acrylic and glass.

The main reason glass is used for aquariums is because it is clear, rigid, and scratch resistant. There is no practical manufacturing process to make a one piece molded clear aquarium in the variety of shapes and sizes that we offer. However, for aquarium sump use it does not matter what the clarity is of the tub so long as you can see your water line. In fact, having less clarity is an advantage as we explain above. Once you eliminate clarity from the necessary features, now weight, strength, and overall integrity of the material are the key factors. Because our HDPE tubs are one piece molds which make them stronger than glued / welded acrylic, and they are much lighter and easier to manipulate, drill holes in, etc. than glass, it makes it the perfect choice for aquarium sump material.