This Nori feeder is easily printed in five parts. The back, front grid, and magnet cover for inside the tank, and the corresponding outside-tank magnet enclosure. It is designed for the 32mm x 2mm magnets commonly available online.

Usage: One half sheet tall (3.9", 10cm) by one strip wide (2.75"/7cm), this feeder can fit 8-10 sheets for your hungry critters.

Feed only what your fish can consume in a 1/2 hour or less. Use a 1/2 strip of Nori for a few fish, multiple strips for a larger feeding. Fold the sheet(s) in half and place in the feeder, then place in the tank. Keep it on the glass with the external magnet. The rear slit is for viewing when it is on the front of the tank, so you can see when it has gone empty.

With one magnet on each side, it will work on glass/acrylic up to 3/8" thick. For thicker material, use the double magnet cover and two magnets on each side. Remove the feeder after feedings for the longest life.

Print in ABS or PETG for the longest life, but you can expect a year or more of use out of PLA if you get the magnets sealed up well. Glue in the magnets with a layer of silicon sealer on top/bottom of the magnet cavities, then spray with multiple coatings of Plasti-Dip.

Files if you'd like to print your own: Thingiverse