Water Weight: Dry Rock vs. Live Rock

Discussion in 'Live Rock' started by Seano Hermano, Feb 18, 2011.

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  1. Seano Hermano

    Seano Hermano Giant Squid

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    The recommended amount or rock for our aquariums is about 1 - 2 lbs per gallon. I am assuming this s for live rock?

    Live rock has water weight, technically making the rock weigh less than what we get charged for. But when we by dry rock, we are buying just that...rock. So, one could say that 75 lbs of dry rock is more rock than 75 lbs of live rock.

    I know that people say to buy a small amount of live rock and buy the rest as dry or base rock. But when I place the two in my tank, pound for pound, the dry rock will displace more water than the live rock will. What I am getting at is couldn't I assume that once I have my initial rock cultured, that I wouldn't need as much total rock(in pounds) if I buy the rest of it was dry rock?

    It seems to take up quite a bit of space. Maybe I just have dense rock.It's very porous though...
     
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  3. FaceOfDeceit

    FaceOfDeceit Hockey Beard

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  4. Seano Hermano

    Seano Hermano Giant Squid

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    See, that's what I was thinking. :) Dry rock displaces much more space. Do you think I would be fine with like 50 lb in my standard 75g?
     
  5. Crimson Ghost

    Crimson Ghost Blue Ringed Angel

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    OK, I understand you – and agree, the good old weight scam ! lol

    I never followed the rule of thumb on rock myself, it’s a matter of opinion. Some folks want the tank chocked full others want just an island of rocks – its just not one of those one size fits all deals. Anywho, yes – if you went at in in mathematical terms after you cultured your rock you wouldn’t need as much total rock poundage if you buy the rest dry.
     
  6. Powerman

    Powerman Giant Squid

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    What kind of rock do you have.

    Yes wet weighs a bunch more than dry. Never really thought about the recommendation.

    Dry will "displace" the same amount of water in the tank as wet. It just weighs more out of the tank.

    I know I wanted as much rock as possible... but actually 2 lbs per gallon is a lot of rock in a tank. I think the PO had about that and I finally took some out cause it was just too much.

    This is all for reef rock.... if you have stuff like Texas holy rock or lace rock, it is much much more dense and will weigh a lot more. The rule of thumb does not apply. You could very easily end up with 2 lbs./gallon and yet not have much rock and not have very much porosity at all.
     
  7. Crimson Ghost

    Crimson Ghost Blue Ringed Angel

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    Well don’t get too jiggy with it – base doesn’t displace any more than live rock. You are just stating that base is absent of water and will thus have more water to fill with. Regardless 50 pounds in a 75 gallon should in my opinion be perfect.
     
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  9. Seano Hermano

    Seano Hermano Giant Squid

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    OK, thanks. My 29 is packed pretty full( 8 lb live, 29 lb dry). I think I want 2 main islands for the 75. I want some open space to place stuff on the sandbed.

    ...With a plane crash in the middle. It should be cool to see it cover in coraline. :)
     
  10. FaceOfDeceit

    FaceOfDeceit Hockey Beard

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    It also depends on the type of rock you get. I've used Marco and Pukani...and the same size of Pukani weighs CONSIDERABLY less than the Marco did. Pukani is VERY porous and has tons of holes for smaller fish (Gobies/Jaws/Blennies) to swim through.
     
  11. Seano Hermano

    Seano Hermano Giant Squid

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    *Huh, hmm*...alright the dry rock displaces the same amount (generally) per pound (not taking density into factor). 1 lb of dry is still the same as 1lb of live rock because with live rock there may be (exaggerated example) 1.75 lb rock and .25 lb water weight to equal a 2 lb rock.

    But what I meant was...the actual rock(dry vs. live)...dry rock "weighs" more(no water).haha
     
  12. Seano Hermano

    Seano Hermano Giant Squid

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    I think it is lace rock. I got 8 lbs lace rock the other day and it looks similar to what my LFS just calls dry rock.