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Heavy Rocks - Any Concern?


8 Feb 2009
I’m still trying to decide on a scape for my AS 900, it’s on the AS cabinet.

I’ve been really loving stone dominant scapes recently, not Iwugumi per se but more like the amano planted monolith scapes.

I’ve been playing in my scape box. I’ve got some big chunks of shale. I will probably have sand or gravel in the middle canyon. Probably use substrate in the areas occupied by the smaller stones.

The big chunk on the right is pretty heavy. I think ideally I want it higher but am worrying about a couple of factors:

Could the whole lot be too heavy for the cabinet?

How should I base the big rock, other rocks, styrofoam, yoga matt?




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In my experience, you could park a small car on a cabinet. They really are stronger than they appear as long as the forces are always downward.

As for the rocks, as long as they have a good base spreading the weight and there's no pressure points on the glass I can't see it being a problem. I remember seeing a video of a guy on Youtube placing a 60L on two bricks at each end, then stacking about 150kg on a singular brick in the centre of the aquarium floor. Didn't even flinch.

I'd go with what you have there with the smaller rocks under the larger one but have a mat under them. Nothing drastic, 5-10mm. Not sure if mylar is aquarium safe, but that would be the best bet if it is. I think the yoga mats are made from it anyway, but some people claim it contains metals.

Another thing to take into account is the tank - is it raised floor or flat? If it's flat then you're laughing. The glass will just transfer the forces straight to the cabinet nice and evenly as opposed to round the sides of the tank.
Thanks for the advice and reassurance!

Think I will go with a few layer of some black yoga mat. Easier to hide than Styrofoam.


Thinking like this ADA scape but bigger

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Not sure on the loads and forces in detail but I used a sand base to bed my rocks into (no where near as big as yours though)

In the tank that it, Helps sit the rock even and not have to load directly on the glass where it could be point loading it.

Not only is the weight a concern the large rocks take up plenty of water capacity.

I have seen a very few DIY cabinets that could easily hold over a massive weight. A big majority have no idea of construction or design. Speaking from Experience as a Retired Cabinet Maker and trade Teacher a total of 36 years.

I’ve recently set up a six foot Mbuna tank at work, with some big chunks of granite, and used egg crate under them.

In the previous incarnation of this tank, I used polystyrene sheets, but the fish exposed them and started chewing on them, resulting in polystyrene balls floating everywhere! It was a pain in the backside.

Are yoga mats fish safe? They’d be a good shout, if they are.

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Thanks for the input.

The cabinet is on a downstairs concrete floor, so no concern there. It is the proper EA cabinet, not something I made myself, Looking at the internal construction all the weight goes through the sides and back panel:


The rock itself despite having a big divet on the bottom is still pretty hefty. 40 Kg on bathroom scales.


Yes, I shouldn’t be picking something like that up with no toe protection

Should I even consider this or should I think of emulating the scape with lighter Lava rock??

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Nothing stopping you putting a bit of 2x2 in the middle behind the doors for peace of mind. Will stop sag as well over time.

Only has to be wedged in there, fixing it in place won't be necessary.
That’s a BIG rock! Should be a 2 or 3 man lift getting it in the tank to avoid accidents. I look forward to seeing this develop
I suspect the verbal weight is fine - but I’d want to support the rock more evenly rather than just the 2 “edges” that would contact the glass, this is easily done by placing a porous stone such as ADA PowerSand or JBL Volcano Mineral in mesh bag (again pay attention to any seams, placing these up into the rock rather than against the glass) & shaping this to fill in that space (so rock sits on glass with more weight distribution)

As Keith mentions, I’m always very cognizant of water volume loss to hardscape, also swimming space ... that’s why my aquascapes are pretty much :oops:
Fish happily utilize the narrow spaces within dense plant zones, not so keen on hanging inside rock ;)

If you haven’t already done so, I’d place the main rocks inside tank, flood, turn on lights & consider the aesthetics ... those ADA Iwagumi stones tend to be uneven in texture & color, with angles & cracks so you get lots of light play/shadows
(obviously do this without substrate for ease, also place that yoga mat on the bottom ... not sure I’d actually use one long term inside tank re compounds entering water column but that’s really a justincase scenario - I have extraordinary luck so know I’d get the single yoga mat sprayed with insecticide (for transport))
A little side note large heavy tanks if on a wooden floor always check under the floor to make sure it can take the extra weight, also check the level of the floor.

If its a rental home/unit check to see if you are permitted to have the extra weight on the floor.

I would be trying to scrub that fungus stuff of the rock! ? I have used a 20kg rock in a 45p tank before, had no problems until the rock fell over (was ambitious with the angle I set the rock on)

IMG_9622 by Colm Doyle, on Flickr

As other said, rather than use a matt or foam under the rock use either crushed lava stone, cat litter or even sand in a filter bag, this will form to the bottom of the stone and distribute the weight more evenly
Thanks for all the input guys. Wow Colm, must have been a bit scary when that big stone went over

Hope the you tube link works, but around 13 mins on the ADA movie they do a scape with 3 big stones. The call them Unzan and it looks like very porous, volcanic rock. Looking at the guys lifting them they are not that heavy. Wonder if similar large volcanic rocks could be sourced here?

I would need an army of Amano helpers to safely get my rock in! I’m still on the fence about this one. The water volume displacement is another good point, that’s 40 L less circulating volume. At least with lava rock it’s full of holes bacteria can use.

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Need to spend more time staring at the tank....


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Yes, just watched it. Interesting position as George says. Personally I would prefer a moss encrusted tower!

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Scape at 2:20 is a totally amazing piece of stone/emergant growth. Wondering how he got that to grow and then not wilt in normal room humidity?

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Thanks for all the input guys. Wow Colm, must have been a bit scary when that big stone went over

Lucky it kind of tipped / fell when I had my hand in the tank, there was not way to re-stable / establish the big rock after this so had to pull it out and rescape, something to consider, make sure everything is very stable before you scape / fill the tank.
I'm from a marine reef background and have done plenty of custom scapes using large live rock structures. The main worry for me is stability rather than weight as it's easy to spread the weight over the base by positioning and support. I once had to do a scape for someone in a 6ft high tank and the rock bommies we created were several hundred kilos each. We cemented the rocks together and placed them on starboard to spread the weight and stock pressure points.
I'd be inclined to use some egg crate on the bottom before covering it in your packing material, as this will spread the weight more and provide a cushion to the tank base. Koi eggcrate is pretty strong.