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I was looking for some small half-tubes for my 5-gallon tanks; most of the ones I found were larger than I needed. I also wanted something made and sold in America instead of waiting weeks for something overseas.
However, along with the half-tubes I found the shrimp houses that my RCS LOVE! Mine are from 4"-6" high.
I didn't include the web site because I wasn't sure it was appropriate.
I imagine if you asked Brantley would make what you need; he did for me. He might even make them in different colors. My RCS were all over the towers and then, suddenly, it was as if they figured it out and three popped into a hole. Now it's like they're playing.
Guess I'm going to have to get a 20L and divide to accommodate the tubes, towers, driftwood, plants, oh, and the shrimp and Si and Willie, the Bettas. :-D