I got a 3d printer as a trade for corals. Flashforge Creator Pro. A little older unit and not super fancy but it was a fun, but sometimes frustrating, learning experience. You need to tinker with calibrating parts of the printer, finding the right temperature for the material you're using, tweaking the print (3d slicer) settings for best results. Really disheartening coming back after 5 hours to check on a print in progress only to find it a big globby mess. Once you get the hang of it it's a really fun and handy tool to custom make things you need. Even for non-hobby things around the house it has been really useful for me.
I have no engineering or design background so I used FreeCAD, which is free, and looked up a bunch of YouTube tutorials on how to 3d model. Some miscellaneous things I've created for the reefing hobby:
Bracket to hold my mangrove plants while they're developing roots
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Frag plug stand for the jars I use to keep frags upright. Useful for like torches and hammers.
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Riser for frag plugs, to encourage frags to branch upwards and because I hate when the corals end up encrusting all over the eggcrate.
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