CopperBand Butterfly Feeder
Print in PETG or reef safe filament. You'll need to insert magnets mid print.
Here is the magnets i used, you can also find them for cheaper online. Also you can resize in 3D software for different sized magnets, just make sure they are strong enough.
There's also a rubber O-ring to grip the glass on the outside Mag Assembly, i used this O--ring kit on Amazon.. I forget exactly which size one it is, but just play with the sizes until one pops in tightly, you may have to convince it in there!
** updated with a hole for a baster to fill the feeder so you don't have to remove the feeder as often.