Holdfast, imo, works better than anything else for frags, rockscaping etc. Especially since you dont have to remove anything from the tank, and you can work with it underwater....
"Build a cascading waterfall, construct an underwater landscape with live rock and coral, create steps, caves, cliffs, and walls for reptiles to enjoy. Explore the limits of your own decorative imagination with HoldFasT. Non-toxic and easy to use, Holdfast activates in the palm of your hand and dries within 30 minutes.
No messy liquids to measure and mix - just break off a piece, knead it until it turns white, and it's ready to bond...even under water! Workable for at least seven minutes before it begins to harden, HoldFasT smooths or sculpts to resemble the surrounding rock, wood, slate, or other environment. And it can be sanded, filed or drilled within one hour of mixing. "
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