Average unit weight of Live Rock

[MikeS]

Hi all...

I'm trying to get an idea of how much crushed LR I'm going to need to make a 4 inch substrate in my 75. By my calculations on the tank dimensions, I'll 2 cubic feet of crushed live rock to do this. Does anybody have a ballbark idea how much "average" live rock weighs per cubic foot? I'm aware that live rock comes in a wide range of densities, I'm just looking for a rough average here...

MikeS

 

[Scooterman]

Guess here but also the density of your rocks (the actual sized crushed average) I'd guess at least 30lbs Very Roughly

 

[MikeS]

yeah, I'm guessing between 30-50lbs per cubic foot, depending on the rock...I can go with a somewhat lower unit weight when figuring the crushed up end product because of the voids between the rock...just trying to get an idea of how much I'm going to need...

MikeS

 

[Scooterman]

Don't you think the crushed rock idea would hold detritus easily?

 

[MikeS]

my hope is to keep as much of it suspended in the water column as possible with good flow through the system, particularly across the bed itself. Also, regular vaccuming of the upper layer will be in order as well to remove as much particulate accumulation as possible.

Mojo Mike is going through the specifics of properly setting up a Jaubert style plenum system with me for my new tank as an alternative to the DSB...using a coarse grade substrate (4-6mm) and good water flow will be in order to keep the system free of relying on bugs and worms to take nutrients to the depths of the bed and plenum to be processed anarobically. Anyway, the use of crushed live rock as the substrate instead of coarse aragonite came up as an alternative.

MikeS

 

[Scooterman]

I remember having a UGF on my fw tanks, I kept one running ten years, never crashed, had pepples. I did vacuum & wc though, and scrubbed the water with floss & carbon.

 

[MikeS]

This will be a "static" plenum in terms of water flow...only the water that reaches it by diffusion will be introduced...no mechanical assistance of flow through the plenum itself. I will however, likely put a sealed riser tube on it somewhere, so maybe once every year or so I can remove some of the accumulated wastes and nasties in the plenum via pump...

MikeS

 

[Scooterman]

Actually I did it both ways, one was pushing air down a tube to create a flow through it, the best way was sticking a PH suction in the tube and sucking water through the plenum, this drew the waste into the pebbles down to the bottom, I actually have one going at a friends house now almost 5 years.

 

[tigerjace]

This is more for calculating sand but gives you an idea. maybe reduce the total amount needed by 1/3 or half from your calculations depending on the coarseness of your substrate. Remember its better to have excess then not enough. http://www.garf.org/calculators/SandBedCalculator.asp

 

[MikeS]

Sand is likely going to have a considerably higher unit weight than 3-5mm crushed LR, far less voids in the sand. What I'm going to do is get about 90lbs and crush it up piece by piece until I have the same volume (about 2.5 cubic feet) in the cure tub...I'll add the excess to the new tank, maybe even enough left over to start a nano...

MikeS