Aquarium Mini Automatic Water Top-Off (for Small Aquariums)

🐟 Fish Tank Mini Auto Top-Off

An automatic top-off enclosure kit designed specifically for desktop mini fish tanks. It automatically refills when the water level is low and stops when the desired level is reached. Compatible with 6-10mm tank walls, it uses L-shaped hooks for installation, is powered by Type-C 5V, features a built-in N20 miniature diaphragm pump, and works with an external float level switch (M8/P25) for automatic water level control. The overall unit dimensions are only 40 × 16 × 52 mm

⚠️ Electronic components need to be purchased and soldered by yourself, does not include accessories like water tubing or a water bucket

✨ Design Features

• no supports — all round holes are designed as teardrop holes
• Fully solid wall thickness — 2.1mm / 5 walls, 0% infill means solid
• Sliding cover enclosure — back panel sliding cover, easy for maintenance and disassembly
• Wave baffle — prevents frequent sensor triggers from water surface fluctuations
• Modular — main body, sliding cover, bracket, tube clip, wave baffle are printed independently

🛒 Accessories List (with reference cost)

💡 The following are electronic/hardware components that need to be purchased separately; 3D printed parts are not included here

🔔 Total cost (including filament) is estimated to be around 15 CNY

🖨️ Printing Recommendations

Filament Selection

Highly recommend PETG, this device will be in prolonged contact with moisture; PLA will absorb moisture and become brittle

Slicer Settings

Print Orientation

🔧 Installation Guide

Step One: Print all parts

• ☐ Main body × 1
• ☐ Sliding cover × 1
• ☐ L-shaped bracket × 1
• ☐ Tube clip × 2
• ☐ Wave baffle × 1

Step Two: Assemble the main body

1. Install the pump — From the rear opening of the main body, place the N20 diaphragm pump into the internal frame
2. Thread the wires — Thread the pump wires and float switch wires out through the wire holes in the main body
3. Solder the circuit — Three components are wired in series, connections are as follows: Positive line: Type-C VBUS(+) → N20 Pump(+) Negative line: Type-C GND(-) → Float Switch → N20 Pump(-)
4. Install the Type-C — Embed the soldered Type-C female connector into the bottom boss slot, secure with glue
5. Close the enclosure — Organize the wiring, slide the cover from the **top** into the slot

Step Three: Install on the fish tank

There are 4 M4 screw holes on the hook baffle; before use, expand all holes with self-tapping screws:

• 1 hole on each side (26mm spacing) — for clamping the main body to the tank wall
• 2 vertical holes in the middle (10mm spacing) — for fixing the L-shaped bracket

Installation steps:

1. Use an M4 self-tapping screw to screw into each of the 4 holes to expand them, then remove
2. Hang the L-shaped bracket on the inside of the tank wall, align the adjustment slots with the 2 middle holes, loosely secure with nylon screws
3. Install the float level switch and wave baffle on the L-shaped bracket (nut fixed)
4. Slide the L-shaped bracket up and down to adjust its height so the float is at the target water level, then tighten the middle screws
5. Hang the main body on the outside of the tank wall, use M4 nylon screws through the side holes to clamp and secure it to the tank wall (do not overtighten)

Step Four: Connect the tubing

1. Connect one end of the silicone tube to the pump outlet, pass it through the top water outlet hole, and bend it into the tank
2. Place the other end into the top-off water bucket
3. Secure the tube firmly with tube clips (stick to the side of the enclosure)

Assembly Tips

• M4 screw holes are pre-drilled to 3.8mm; first, use self-tapping screws to expand the holes, then remove them and use nylon screws to fix
• Do not overtighten when screwing; stop when you feel resistance to avoid cracking the printed part

📖 Usage Instructions

Daily Use

1. Plug and Play — Connect Type-C to a 5V power source (charger / power bank will work)
2. Automatic Operation — Water level drops below float position → pump starts refilling → water level restores → pump stops
3. Refill Bucket — Regularly check the water level in the top-off bucket, remember to add water when it's empty

Precautions

• ⚠️ The water level in the bucket should be **below** the fish tank water level to prevent siphoning backflow
• ⚠️ For first use, it's recommended to **monitor it for a while** to confirm the float switch sensitivity and refill volume are normal
• ⚠️ Regularly check the silicone tube for aging, kinking, or blockage
• ⚠️ It's recommended to cover the top-off bucket to prevent dust and insects

Troubleshooting

❓ FAQ

Q: Can it be printed with PLA
A: Not recommended. PLA becomes brittle after absorbing moisture, and prolonged use near a fish tank may cause cracking. It's acceptable for temporary use, but PETG is more reliable for long-term use

Q: Is a waterproof coating necessary
A: No. A 5-wall PETG print is inherently waterproof, no extra treatment is needed

Q: Can it be adapted for larger fish tanks
A: This design is compatible with 6-10mm tank wall thickness. If the tank wall is outside this range, you'll need to adjust the hook spacing yourself

Q: How to wire the float switch
A: Very simple — the float switch is connected in series with the pump's power circuit. Low water level → float sinks → switch closes → pump powers on → starts refilling

Q: Is it noisy
A: The N20 diaphragm pump operates very quietly, similar to a phone's vibration, barely noticeable in daily use

🎣 Keeping fish should be an easy thing. Let the machine handle small tasks like refilling