Fluval AC20 Flow Deflector – Betta Friendly Mod

Fluval AC20 Flow Deflector – Betta Friendly Mod (PETG)

This custom flow deflector is designed specifically for the Fluval AC20 hang-on-back filter and is optimized for low-flow aquariums, such as betta tanks (bettari) and other small or calm-water setups.

The goal of this mod is simple:
➡️ reduce surface turbulence,
➡️ spread the outflow more evenly,
➡️ protect long-finned fish like Betta splendens from excessive current.

Key Features

• Gentle flow diffusion
  The water outlet is redirected and diffused through multiple side and front holes, reducing direct current while maintaining good circulation.
• No bottom holes
  The bottom section is solid to prevent downward jets and substrate disturbance.
  Flow starts gradually from 1.5 mm up to 3 mm holes, distributed laterally and frontally.
• Designed for betta aquariums
  Ideal for long-finned fish that struggle with strong currents. Helps create a calmer, more natural environment.
• Plug & play fit
  Designed to mount directly onto the Fluval AC20 outlet without permanent modifications.

Printing Notes

• Recommended material: PETG
  (better water resistance and long-term durability compared to PLA)
• Supports: Yes, required
• Orientation: As shown in the photos
• Infill: 20–30% is sufficient

Important Note

For best results, this deflector is intended to be used together with the custom AC20 filter basket available on my MakerWorld profile.
Using both mods together significantly improves:

• flow control,
• biological filtration efficiency,
• overall betta comfort.

Disclaimer

This is a user-made modification and is not affiliated with Fluval.
Always test flow and fish behavior after installation.