Check out the latest guide from Erin St. Blaine: decorate your fish tank or aquarium with color-changing lights. This tutorial shows how to assemble and waterproof your NeoPixel lights so you can bury them under seashells or sea glass at the bottom of your fish tank. It includes Arduino code that allows you to change between animated color modes with a touch of your finger, using a decorative strip of copper tape as a capacitive touch sensor.

This build uses a QT Py microcontroller, a strip of 144/m NeoPixels as an above-water light, and a strand of NeoPixel dots submerged in the water for a unique underwater glow.

From the guide:

Decorate your aquarium with NeoPixels. Add a high density strip of lights above the water for a beautiful overall colored glow, with subtle color shifts and changes. Cycle between color modes to suit your mood, the time of day, or to signal feeding time.

For an extra special bit of underwater magic, attach a NeoPixel Strand and submerse the lights under the water. Diffuse the lights with seashells or bits of colored glass to complete the effect.

This DIY solution will cost you a lot less than the prepackaged aquarium LED light kits available at the pet store, and will give you a lot more control over brightness, color modes and customization. But it’s the addition of the submersible strand that really makes this project special, and will make your aquarium stand out from the crowd.

See the full tutorial here: https://learn.adafruit.com/neopixel-aquarium-with-submersible-lights/overview