Gravel & Weight

[coldmachineUK]

Hi, I wondered if I could pick people's brains on this one.
I've seen various recommendations for amounts of substrate all over the place, and wondered what people thought about these:

1. Use only 2" of gravel.

2. Use 1 pound of gravel for every 1 gallon of water the tank can hold

3. Use a stand which can carry 10 pounds of weight (=1 gallon of water).

My question is: is there a hard and fast rule to how much substrate to use? I ask this because I've seen people using sand (is sand lighter than tiny pea gravel?) and making sculpted substrates with it (i.e. troughs and peaks), and wondered if gravel can be used to the same effect?
A friend is setting up a 6'x2'x2' tank and this will factor in to advice for that

 

[rich311k]

I think it is entirely up to the owner. The weight should not matter, look how much rock some of us pile into a tank. If the stand is made for the tank, extra gravel to make a slope will not make difference in the overall stability of the physical system.

 

[coldmachineUK]

Ok, well I've gone with a gradiated slope then :S I actually buried two caves in the slope too...! Wish me luck!

It's for a cichlid setup (I posted a different thread about stocking levels), so I am trying to make it a bit more natural for them and give them space to dig and burrow. I bought 25KG of very very fine gravel (smaller than pea even), and used about half of that along with a much larger (larger than pea! lol) type underneath. I opted for gravel rather than sand, because a friend uses only sand and I believe some of her problems stem from maintenance of that (I like my gravel vacs What can I say? lol).

I will get a picture up soon, pre stocking levels, to ask for people's advice. There's a ton of lava rock in there too :S Not literally a ton Just seems like it
I have heavily aquascaped b/c the tank is only a 40G 33" long (custom) tank, so I was advised to do so in order to reduce the associated aggression...wish me luck!

It's on a purpose built stand, and on top of a very thick layer of polystyrene too...hopefully that will distribute the weight as well.

Edit: Here are a couple of pics. The plant pot is what's containing my prawns right now for the fishless cycling. There are two white spar rock caves in the slope (one at the front, facing towards the back of the tank, is covered by a small piece of lava rock at the moment).
I am going to plant some vallisneria around that side, and towards the back left.

You can see the polystyrene here:

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[hc8719]

looks good

personally i dont use alot of substrate, just enough to cover the bottom of the tank really, crud always gets stuck down there and none of my fish move the rocks around, depends on the fish and their bio-load i guess

 

[physicsdude]

Well, what I worry about is pressure points on the glass cause by buildup of heavy rocks on small areas of the aquarium's bottom. Theres a great website that I would just like show everyone regarding weight issues and placements of aqauriums in homes:
http://badmanstropicalfish.com/articles/article28.html
I know this is a tangent from the core of the article, but with all the weight described and pictured here, I just thought I would pass it along.

 

[coldmachineUK]

Hi there,

Great article! I have bookmarked that for future ref
The lava rock is actually very light: a reason I picked that rather than anything else. I actually had to wedge some pieces together to keep them down because they're quite bouyant. Though, some other pieces are quite heavy. Also, I noticed when I move them around in the tank they're light (I can move one with a couple of fingers no probs) but when I pull one out of the tank it becomes heavy and I need one whole hand (or both). The water is exerting forces in all directions, including upwards, which is why it's bouyant also and this might lessen the load on the bottom pane some.

The room itself is capable of taking this load: here in the UK most of our houses don't have basements (only old townhouses usually), and this is all in a downstairs room. I don't know the load levels precisely though: now I've read that article I'm going to go find out!

Also, I've read that adding rock to a tank will displace some of the water. So, if your rock weighs less than the same volume/mass of water, it would actually be lighter than having just the water. How true that is, and the precise weight of lava rock/gravel vs. water, I have no idea!!!

Edit: I forgot to add; you should see I've also reduced the amount of lava rock on the side which has the highest levels of gravel, in order to balance the weight a little more too.

My main concern was the gravel rather than the lava rock...so far no cracks, leaks or explosions :S Fingers crossed... :S

EDIT:
Ok, a quick update: I have redesigned the tank completely. Better to be safe than sorry! I've removed one piece of lava rock + one (smaller) of the two caves, and have also removed a ton of gravel and reshaped it.

Pics:

Do you think this is better? I don't think it looks as great...but it will be less load at least.