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Basic Plumbing for a 90 gallon Saltwater Aquarium


90 gallon saltwater plumbing

I recently had the privilege of building a 90 gallon fish-only saltwater aquarium setup from nearly scratch. I found that if you prepare, and perform the appropriate research, it is a relatively simple process.


The client already had a 90 gallon tank, drilled with a 1” and a ¾” hole in the bottom with an off center overflow, and a 40 gallon breeder sump with 3 baffles installed.


To complete this project I would need to (1) build a stand that could accommodate a 90 gallon aquarium with an 18 inch deep sump. There are no prefabricated aquarium stands for a 90 gallon tank that would fit an 18 inch sump underneath.


Next, (2) I would need to design and configure the plumbing to achieve an intake, stand pipe, and return. This would require some extra thought, as there were only two holes drilled instead of the three required.


Finally, (3) the remaining hardscape and equipment need to be laid out and installed.


Planning and Designing the Aquarium System

The key to successfully building a plumbed aquarium system with a sump from scratch is to focus on the planning stage. Nothing is more expensive than purchasing all your plumbing, equipment, and beginning to glue things together, only to discover your sump is too large, the skimmer is too tall, the return pump is too small, and you have twice as many gate valves and half as many unions as you need.


As I go through each section, I’ll discuss how I accounted for everything I could think of during the planning stage. For example, when building the stand, I needed to account for where the holes in the tank were so I didn’t install a support right where the plumbing would go.


Building a Frame Stand for a 90 Gallon Aquarium

I chose the frame only design for this stand to expose the sump, plumbing, and components underneath. This system was installed in a school and every component acted as a teaching tool.


I had never built a stand before. So the first thing I did was go online and search for videos, designs, and blueprints of homebuilt aquarium stands. At this stage I wasn’t concerned with any details. I wanted to familiarize myself with the process, gauge the level of difficulty, and estimate the number of tools and materials I would need with approximate cost.


After I learned what a well-built, successful aquarium frame stand looks like, I began to dig a little deeper and learned about miter saws, the weight capacity of a 2x4, live vs. dead weight, and the importance of maintaining a level build throughout the whole process.


When I was comfortable with the idea of building a stand myself, I started to look into specific plans and blueprints available online. I quickly came across one for a standard 75 gallon which has the same length and depth as a 90 gallon. The plans I settled on were detailed enough I felt comfortable using them to build my first frame stand without fear of missing any important details or materials.


I altered two details from the original plan. I moved the cross brace locations in the top of the stand as it would have been directly under where the overflow was to sit and therefore block the plumbing. I also added and adjusted the positions of the cross braces on the bottom. Without plywood covering the bottom, the sump would need to be supported underneath by boards on all four sides, so I adjusted the cross braces so they would rest underneath the two sides of the sump.


I then calculated the amount of 2x4s I would need, plus an extra board, and the number and type of screws. I then purchased a miter saw and table, and the materials.



It took me about 6 hours to put the stand together. It came out level, minus a few places where I sanded down. At this point, I decided I wanted to finish it with a black exterior paint. After a quick sanding and two coats of paint, the stand was nearly finished.


The last component was adhering a strip of ⅛ inch neoprene foam padding onto the top of the stand and the bottom portion where the sump would sit. This acted as a cushion and self-leveling pad.


Simple Plumbing for a 90 Gallon Saltwater Aquarium

I wanted the plumbing to be as simple as possible for this setup. I forwent manifolds and extra pathways for water changes and just stuck to three main sections. (1) the intake, (2) the stand pipe, and (3) the return. It should be noted, I designed the plumbing before I built the stand.


I started by taking dozens of photos of the tank, sump, and overflow. Then I measured, remeasured, and measured again each and every part of the aquarium and sump. I took the normal length, width, and height measurements. I also considered the height of the top and bottom of the aquarium if it were on a 30” stand, and the distance between the top of the aquarium and the top of the sump if the sump was 3 inches (width of a 2x4) from the floor .


I measured the length, width, and height of the overflow at the center and on the sides as it had a curved opening. I measured the distance between the overflow and the left and right side of the tank, the distance between the overflow and the cross brace, and even the distance between the pre-drilled holes and the back glass pane of the aquarium.


Simple aquarium plumbing

Then I sat down with a whiteboard and used color-coded pens to draw (not to scale) a rough schematic of the plumbing. This drawing included what fittings would be used, their size, thread or slip, and their location.


I had two schematics drawn up; they differed in the layout of the return outlets and their placement. One had them on either side of the aquarium and the other had them both coming out of the overflow. I decided to go with the second design as it would mean less 90 degree fittings (higher flow rate) and less materials.


I returned to the design several times over the course of a week and followed the flow of water through the schematic and thought about how each section would affect the flow and how each fitting would impact the design. I wanted plenty of unions to facilitate disassembly if necessary. I also wanted a gate valve at the intake and the return to control overflow volume and flow rate respectively. I wanted to make sure threaded fittings were used where possible to ease any disassembly that might be required as well.


After I was finally satisfied with the schematic and my materials list, I purchased everything and after it all arrived I double checked to make sure I had everything I needed. I ended up only having to purchase one more female slip x thread coupling; not too bad.


When I arrived on site, I measured, cut, and assembled the plumbing according to the schematic without gluing or taping anything. When I was satisfied with the plumbing, I then disassembled and glued or taped each section ( intake, stand pipe, and return).



When I was finished, I fastened the return section to the back of the stand for stability and was lucky enough to have everything align perfectly. The return pump was hard plumbed with no soft hosing and it required very little height adjustment after the fact.


I waited 24 hours and began the leak test by filling the tank and sump with RODI water without any equipment installed except the return pump. I plugged the pump in and returned in another 24 hours with no leaks or issues of any kind.


After the plumbing and aquarium had proven it could hold water without leaking it was time to install the rest of the equipment and add the gravel, rocks, and salt.


90 Gallon Saltwater Aquarium Hardscape

As a fish only system, I didn’t want anything too complicated for the rock work. I wanted to create fish-centric habitats with plenty of open spaces to swim. I used approximately 95 lbs of various dry, live rock I had accumulated. I bleached the rock for a week, then rinsed in a RODI + Prime bath twice. Finally, I let it air dry under two commercial blowers to evaporate any remaining bleach or chlorine.


The client also wanted a few pieces of fake coral and they were easy enough to come by. The dry, live rock I used also included several coral skeletons.


Filling a saltwater aquarium

Fish only saltwater aquarium



After the leak test, I drained 80% of the RODI water into two 40 gallon Brute trash cans. I then mixed 100 gallons worth of salt in the cans while I layed down a layer of aragonite gravel and placed the rockwork. I used RODI water for the leak test so I could simply add salt and not have to drain out every drop of tap water.



I then refilled the aquarium and began to install the equipment.




90 Gallon Saltwater Aquarium Equipment

As a fish only system, the lighting requirements were very simple. I chose a 48” LED fixture with dimming capabilities and several color options. I placed a 300 watt heater in the sump and installed the skimmer in the middle chamber. For biological filtration, I added two large mesh bags full of Cermedia Spheres. The physical filtration is a single 4” filter sock nestled in an acrylic sock holder that fastens to the side of the sump. I intentionally lined up the sump, sock holder and intake tube.


A refugium could be added later. Fish only systems arguably need more filtration than reefs because there are no higher organisms, other than bacteria, to absorb nitrates and phosphates. This type of system relies heavily on biological and chemical filtration to keep the water clean.


Finished 90 Gallon Fish Only Setup

And there you have it. The next steps are to begin cycling the aquarium and then start adding livestock when appropriate.


I learned quite a bit from this process and enjoyed every step. To acquire new tools and learn new skills by doing and having something to show for all my effort is highly satisfying. It also helped that I kept the design of this system pretty simple. You can easily upgrade by adding extra plumbing, rolling mat filtration, auto-top-off chambers, dosing systems, etc.


I hope this article provides some insight into the process of designing and building a simple saltwater aquarium. I also hope it relieves some of the inhibition in your ability to accomplish something like this and inspires you to build a system of your own.


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