Thank you for the rating!

my husband loves it for the tanks!

That's great to hear, I wish him success in fishkeeping!

Thank you for liking the idea. Yes, bio-media really sell at premium prices, so anyone who is running a print farm, runs PETG in volume, and can cleanly separate the PETG filament 'poop' can give this a go.

Thanks for your interest! A bit of explanation on the workings first :) The filter works like many air-driven bio filters in the market, by pushing air to the bottom of the filter's core, to rise as bubbles which then draws water inwards through the filter's bio-media. Over a period of time (2-3 weeks typically), beneficial bacteria will colonize the bio-media, in this case PETG waste filament, and help to establish the nitrogen cycle in the tank. The great thing about 3D printing is the entire core structure can be printed as one single part with the filter body, vs several parts in injected-molded ones. Many types of materials are used for the bio-media: ceramics, sintered glass, plastics, even crushed corals. They come in many shapes: rings, balls, pucks etc. The goal is to offer a large but free flowing surface area for the bacteria to colonize. As for the effectiveness between the different types of materials and shapes, it's beyond me to conduct proper comparisons, but IMHO, the filament waste from BL's printers, with their curly yet open structure, should work reasonably well. As for the cons of such type of filter, I would say there will be some noise from the bubbling, and they are more suited for smaller tanks. PS: I've added an animated GIF showing the filter operating in a tank. Cheers!