Calculating rocks and extra weight


New Member
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Just started
Hey y'all! I'm attempting to aquascape a 75 gallon and I'm unsure of how much weight the glass can hold in a more specific area of the tank. With it being a fairly large tank and my first major attempt at an aquascape I'd love any tips on glueing rocks, types of rocks, should I use only resin? Or can the tank support a 20lb cluster of rock on only about 6-8 inches of glass? Tips on plants, personal favorites, easy non co2 needing mosses and "tree top plants".
So I guess mainly how to tell if my aquarium can hold heavy sections of rock and through any other aquascaping tips you want at me!! TIA!


Well Known Member
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5 to 10 years
If you want to spread the weight of large rocks you can place a clean roofing slate on the bottom hidden under the substrate. Make sure it's a natural slate not a man made one and also if it's a used one it wasn't from under a lead sealed window.
Most rocks are OK but avoid anything calcerious such as limestone. If in doubt test with acid ( vinegar will do if you don't have anything stronger ), add a few drops to the rock and if it reacts it's not suitable.
For sticking rocks together I use aquarium grade silicone.
Make sure the aquarium sits on a flat surface and if it's not even place polystyrene ceiling tiles between the surface and glass to take up any imperfections.


Valued Member
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3 years
saltwater60 said:
You’ll be fine. You can basically fill a fish tank with rocks.
Pretty much agree with this. I've heard one story from a friend that had a couple "1 man" size pieces of basalt in a 125. I think that's something like 150 lbs each, maybe 2ft or so diameter. He put them in there when it was half full of water on a bed of sand. Didn't have any issues for a couple years until he was draining the tank all the way down to strip it and one tipped over, made a pretty quick mess. I have read of people building little bases for them out of sealed (pond armor etc) pavers. Put a bead of silicone around the bottom of the paver and let it dry out of the tank like rubber feet, supposedly works pretty well but I've never actually done such a thing.

I have built a little cave using chunks of rock and hot glue though, not had an issue with the glue coming apart that way, Incase you want to build little bases and don't have the patience for silicone to dry, hot glue is an option for this type of thing.
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