I wanted to get my Biospheres out of the mesh bag and up in a rack for easy cleaning, maintenance, replacement, etc. and needed to fit nicely in my Red Sea Reefer XL300's sump. The sump space is about 210mm x 80mm (with the divider wall closest to the back of the sump) so this fits inside that foot print nicely.

The rack can be stacked, so you can print as many as you want and they will stack properly. The tabs on the side braces and the poles fit into the bottom carveouts on the rack above.

Two racks will hold one box of biospheres. Please note: there may be some spheres that require some boring out of the hole to fit because I noticed that they aren't all perfectly circular. In my box, all but two fit fine.

I recommend printing in PETG as its the most reef safe and shouldn't break down as fast as PLA. Also, I printed 100% infill for max strength and two took me 44 hours to print. I don't think it's 100% necessary to print this way, but I wanted to be safe.

Included are feet that help stand off the bottom rack from the bottom of the sump to support water flow under it and limit detritus build up. Print 10 of the pointed ones and 2 of the long feet if desired. I super glued mine in place, but they friction fit pretty well depending on your printer.