I have already talked about liking glass over acrylic aquariums. Acrylic is not a great material for a display tank.

Sumps are a bit different

The primary role of a sump is to perform varieties of water filtration. Most of these tasks don’t need to be seen or heard. The exception to that is a refugium which often needs to be well lit.

Many of acrylic’s disadvantages as a display tank simply don’t apply. It doesn’t matter if it’s scratched or yellow. As long as it is well built, it will serve the purpose. Since it is so easy to work with, building your own sump design is entirely possible with acrylic. Glass is also still great however there is another option in the seamless sumps I talked about earlier.

HDPE as a sump material

HDPE stands for high density polyethylene. You have probably encountered this material at some point in your life. Hood milk jugs are made out of it. It is a very common and safe material for many uses.

As I have discussed before, the seamless sump is composed entirely of this material. Not only that, but the tubs are a single molded piece. This means they are exceptionally strong and will not leak. Additionally, the interior features (like baffles for the media filter/return tub) are part of that single mold. They will not come loose in the future.

The material is still easily drilled (unlike glass). Meaning connecting the tubs together is simple (this is where the only seals on the entire system exist).

Like a hood milk jug, you can still see the level of the liquid inside. This turns out to be both an advantage and a disadvantage.

AdvantagesHDPE Advantages

The material is used in many food and medical industries. Very little can bond with it meaning nothing will stick to the surface. This makes it easier to clean.

The sump will always look clean. From the outside you won’t see all the junk that is intentionally growing inside.


HDPE doesn’t seem like a great solution for refugiums where you might want to see inside or have strong lights. If I am using my refugium to isolate a fish, I probably want to see how the fish is doing. Not great for that. I may go so far as to ask the company to produce a glass cage of the same dimensions and drill holes to add to the seamless sump. That way I can have a great glass refugium to complement the seamless sump system.

The current seamless sump solution is not as cost effective as I would like. This is likely due to a complex fabrication process. This isn’t something you can just make at home.


I really like the seamless sump design. But, for me, I would probably like it in any material. In fact, I would love to see someone build a similar modular design out of glass or acrylic. One of the reasons this likely hasn’t happened is because of fabrication issues and/or cost. Plus, it’s simply easier to just custom build a single sump out of those materials if HDPE isn’t desired.

To me HDPE by itself is not a decision maker. I think long term I will probably appreciate having it. It’s the modular nature of the system that sells me on it. I imagine this is one of those things that might change after owning an HDPE seamless sump.

What do you think about HDPE in sumps?

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