These can fit in the back of HOB filters and boost the bio capacity of any small system with easy. They hold up well over time and I have never had one fall apart/break. I have run them in FW prior but currently running some in the back of my AIO reef aquarium.

I was looking for some bio media to slip into a media bag for the back of my nano all in one tank and these fit the bill perfectly. They're small and pack pretty densely into any space. I would imagine these would be great for filling the gaps between larger media balls when used in larger tanks to really maximize biological media.

I have not yet used these! So bare that in mind. I purchased 3 of these, thinking it might be enough to fill (2) of item 250213 - the 4" Sea Foam media cups... you'll need two of these to fill just one media cup top the top. So, I need to order a 4th one of these. I guess you could leave some headspace in the media cup and fill it with cut-to-fit filter floss if you wanted... Other than that, they look like they'll work well. I'll update my review once I get this thing up and running!

I have a giant pile of these stored in my sump that I use for jump-starting new tanks. I take them out by the handful and replace with fresh ones. Small enough to toss in anywhere you can think of; took out the innards of a HOB filter and stuffed it with these gems and they still allow for optimal water flow. When I'm done using them for QT/hospital I soak them in a bleach solution, rinse, and let them air-dry completely, and they can be safely used again. They go through a lot, and they're still just as sturdy as ever.

A little more surface area than the spheres..easier to clean on the surface.