How To: The Acclimation Box
This Project Reduces New Fish Aggression Mortalities To Near Zero.
DIY Acclimation Box
Quick Summary
We are going to walk you through building a simple, effective acclimation box for safely adding fish to your aquarium. This DIY design avoids the pitfalls of many retail boxes, scales to any tank size, and gives you options for either an egg crate bottom or a drilled acrylic plate. Follow these steps and you can have fish eating and acclimating to tankmates without getting harassed.
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Step 1: Why build a DIY acclimation box?
The acclimation box serves three important purposes:
The acclimation box dramatically reduces aggression toward new fish by allowing existing tank mates to see and get used to the newcomer before release. In many cases this results in little to no aggression, even with territorial species like tangs, and is far more effective than the release and hope approach.
The acclimation gives the new fish time to adjust from wild foods to prepared aquarium foods without having to compete or be bullied, which improves early feeding success.
The acclimation helps minimize stress during introduction, lowering the chance that parasites will overwhelm the new fish’s immune defenses or spread to others in the tank. This is especially valuable if you are not quarantining every fish before adding it to the display.
Why DIY? Retail boxes often have holes or perforations on the sides that can act like a cheese grater as fish pace back and forth. Our design eliminates side holes, reduces sharp edges, and is fully customizable to fit your tank. It also avoids gimmicks like magnetic brackets that can pop off and let fish escape.
Step 2: Gather materials and tools
Here is everything we use and recommend. You can adapt based on what is available locally.
Quarter inch acrylic sheets (sized to your tank). Best from a plastic supply shop with cut service. Home improvement stores stock plastic sheets for quick needs but may cost more.
Glue: Weld-On #16 solvent cement from an acrylic/plastic supply shop. If using hardware store-bought acrylic, you can use super glue gel (not the thin liquid) for a strong, easy bond.
Masking tape (for clamping panels while glue cures)
Carpenter's square (to keep panels square while assembling)
Egg crate lighting diffuser (optional, for a quick removable bottom)
Stepper bit for drilling smooth holes in acrylic (optional, for drilled bottom)
Safety: work in a well ventilated area or wear a respirator when using solvent cement; follow product safety instructions.
Step 3: Choose where to buy acrylic and pros/cons
We recommend checking a local plastic supply shop first. They will cut sheets to size, usually quickly and affordably. If you need something immediately, Home Depot or a similar store carries quarter inch acrylic sheets near the window/door/trim area that you can buy the same day. Expect higher price there but immediate availability.
Note: Harware store-bought acrylic from home centers is usually extruded material and not ideal for water tight applications but works fine for this project. The box does not have to be watertight because the bottom will have holes (or an egg crate bottom) and the goal is structural stability rather than sealing water.
Step 4: Cut list and example dimensions
We built two main sizes in our shop: a 120 gallon box and a small Nuvo 25 corner box. Below are the common tank sizes with the pieces required. Always double-check your waterline and tank trim before final cuts and adjust heights as needed.
40 breeder / 60 cube
(1) 6 x 6
(1) 6 x 8
(1) 10 x 6 (check your tank height; these assume an 8 inch box height with 2 inch water difference to edge)
(1) 10 x 8 (check your tank height)
(3) 8 x 1
(1) 6 x 1
(1) 6 x 7.25 bottom plate drilled with 8–12 holes sized 3/8" to 1/2")
120 gallon
(2) 10 x 10 (check 10” height, adjust to your water level. Currently set at 8” box height 2” water difference to edge)
(2) 10 x 8
(2) 10 x 1.5
(2) 10.5 x 1
(1) 10 x 9.5 bottom plate / egg crate
180 gallon
(2) 12 x 12 (check 10” height, adjust to your water level. Currently set at 8” box height 2” water difference to edge)
(2) 12 x 10
(2) 12 x 2
(2) 12 x 1
(1) 10 x 11.25 bottom plate / egg crate
Nuvo 25 Lagoon
(1) 11 x 4
(1) 11 x 8
Step 5: Prepare panels and remove protective film
Peel the protective paper/plastic film from the acrylic after cutting. It protects the surface during cutting but must be removed before assembly. Inspect each panel for cracks or defects hidden under the film. If you find a hairline crack, decide whether to replace the panel or proceed—the box will not hold water in the bottom so small blemishes are often acceptable for this use.
Step 6: Dry fit and tape panels before gluing
Lay out all pieces and dry fit them first. Cut several strips of masking tape in advance so you can work quickly when applying glue. We assemble by joining the larger panels first and using tape as a clamp. Place tape on the outside face of the panel so you can pull the piece tight toward its mate and keep everything square.
Apply a light bead of glue to the mating edge. Press panels together, use the square to verify right angles, and tape them until the glue sets. A little glue goes a long way; the structural bond for this box is moderate and the tape will hold alignment while the glue cures enough to add bracing.
Step 7: Add bottom ledges and top lip brackets
After the main box is assembled and the glue has set for a few minutes, add the bottom ledges that will hold the egg crate or drilled acrylic plate. Glue these ledges inside the box so the removable bottom can slide or rest on them. Next attach the top lip brackets that will sit on the tank trim or edge. Tape these brackets in place while the glue cures.
These ledges and lip pieces are what makes the bottom removable and what lets the box just hang on the inside trim of your tank without drilling into glass.
Step 8: Egg crate bottom option
The fastest removable bottom is a sheet of egg crate lighting diffuser cut to fit the box interior. It sits on the ledges and allows detritus to fall through while preventing sharp edges along the sides. To size egg crate, measure the interior and score a cut line, then give it a firm whack or use heavy-duty scissors to snap it to size. You do not need to snip every cell individually; measure and cut across the sheet.
Step 9: Drilled acrylic bottom option
If you want a cleaner look or smaller holes, cut an acrylic bottom plate to fit and drill holes through it. Use a stepper bit to drill in steps. A stepper bit cuts acrylic with less cracking and produces a smoother, less sharp hole edge compared to a standard wood bit. Drill from both sides when possible to reduce splintering on the exit side.
Advantages of a drilled acrylic plate:
Smaller holes prevent small fish or shrimp from slipping through egg crate gaps.
Holes can be positioned so food settles and the fish can inspect and pick at it rather than it falling through instantly.
Solid removable plate is easy to scrub and reinsert.
Step 10: Nuvo 25 / small corner box version
For smaller all-in-one tanks, a corner wedge box works great. This is just two panels forming a right angle that wedge into the sand and sit against the silicone bead. In our Nuvo 25 example we cut two panels sized 11 x 4 and 11 x 8. We removed the small corner tabs so the box does not cut into the silicone bead and so it sits flush.
This corner style is simple to build and can be made from quarter inch sheet bought that day at a home center if you need a quick solution. It scales up: similar corner boxes can be built for larger tanks or custom needs. If your system has strong flow, make sure the box is snug or use a clamp or magnet on the outside to prevent drifting.
Step 11: Final checks and installation
When glue is fully set, remove the tape and test fit the bottom plate or egg crate. Place the box on the inside trim, ensuring the top lip sits above the waterline and the bottom sits above the substrate as intended. The box is designed to keep fish enclosed and safe while allowing flow through the holes or egg crate so water quality in the box remains stable.
Suggested acclimation routine in the box:
Keep new fish in the box for several days to a couple of weeks depending on behavior and health.
Feed while in the box to train fish to accept tank food and to let them strengthen before release.
Monitor for aggression through the tank glass; most aggression will subside as fish adjust to visual presence.
Step 12: Tips, tricks, and safety notes
Glue safety: solvent cements and some cyanoacrylate fumes can be harmful. Work in a well ventilated area or use a respirator and follow manufacturer instructions.
When drilling acrylic, use a stepper bit and drill from both sides to minimize splintering.
If you discover cracks under the protective film, decide whether to replace the piece. Small surface chips are often acceptable because the box is not meant to be watertight.
Make the top lip height so the box sits on your tank trim and the waterline in the box is slightly below the tank waterline to avoid overflow.
Use tape during assembly to clamp panels together and keep everything square. Pre-cut strips so you can work quickly when glue is applied.
Final Thoughts
This acclimation box is a simple, practical tool that saves fish and reduces stress during introductions. With a few basic materials and a little time, we can build a better box than most retail options, tailor it to the tank, and keep new fish safe while they settle in. Try one for your next addition and pass the idea on—this small piece of gear can make a big difference for hobbyists and fish alike.
Acclimation Box FAQ
Why build a DIY acclimation box instead of buying one?
DIY boxes let you customize size to your tank, avoid side holes that can abrade pacing fish, eliminate weak magnet or gimmick closures, and usually provide a stronger, more functional design for quarantining and acclimating fish.
Can I use acrylic from Home Depot?
Yes. Home centers carry quarter inch acrylic sheets that are great for same-day builds. They may cost more than a plastic supply shop and might not be cut precisely, but they are widely available and work well for this non-watertight application.
What glue should I use?
If you get acrylic from a plastic supply shop, use Weld-On #16 solvent cement for the stronger bond. If using home center acrylic, super glue gel is a practical, readily available option. Work in a ventilated area and follow safety directions.
Which bottom is better: egg crate or drilled acrylic?
Egg crate is faster and allows detritus to fall through; it is an excellent removable bottom for general uses. A drilled acrylic plate gives smaller, cleaner holes and works better for small fish or when you want food to remain visible on the bottom. Choose based on the species and your goals.
Will the box hold water?
No. The box is intentionally not watertight because the bottom will allow water to flow through. Structural integrity is the goal rather than a watertight seal. The box should be sturdy and sit on the trim so it does not float.
How long should fish stay in the acclimation box?
That depends. Some fish can acclimate in a few days once they are eating and show no signs of stress or aggression. Others may benefit from one to two weeks in the box to recover from shipping, learn to eat tank foods, and get used to tankmates. If you have tangs or aggressive fish, two weeks is a good plan.
Can this design be scaled for large tanks?
Absolutely. The same principles scale up. We have used multi-sided boxes that span top to bottom in large systems. Just ensure the box is snug, supported on the tank trim, and that flow and hole placement are appropriate for the size and species.
Acknowledgments
Thank you to Elliot Lim for sharing his knowledge with the SR community. Thank you to Ryan Thompson for summarizing the video and making it available to everyone.
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