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determining gross volume

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  • determining gross volume

    does anyone know how much space liverock will take up inside a tank? i am planning a new tank and i want the total gross volume to be a multiple of 25 (150,175,200 gallons) so that it is easier for me to get exact doses on the ZEO's.

  • #2
    Greetings All !

    Aged Salt has suggested ... IIRC ... an estimate of around 20% of tank volume if you're adding the "typical" amount of LR to a tank. IME this is pretty accurate, and functions nicely as a ZEOvit dosing starting point. You're going to be adjusting dosing as your system evolves, anyway.

    If you want exactitude (... is that a real word? ...), then measure that SW added to the empty system after substrate (... if any ...) and LR have been placed into the system. If you're mixing SW in a large container, just keep track of "how many" you add. This is the only way to get the "real" number, IMO.

    If you're really into "virtually exact" measurements, then you can use "displacement" as a way to calculate the volume consumed by LR.

    I posted this to a similar question a couple of months ago ...
    Unfortunately, the variable density of LR makes any "real calculation" impossible ... there's simply no way to come up with a "universal" standardized weight vs. displacement equation.

    And yet ... it turns out that you can do some surprisingly accurate estimations for this kind of thing, but it requires a little more effort than most hobbyists are willing to expend.

    For estimating the displacement resulting from the live rock ...
    You'll need:

    A piece of your live rock;
    (The piece may be large or small, as long as it is representative of the LR in question. Multiple varieties of LR will each require a representative sample piece.)

    A container which allows you to read the change in volume;
    (The container can be as "geek-like" or utilitarian as you wish ... anything from a graduated cylinder or beaker, to an average kitchen measuring cup, to a bucket within which you have made marks corresponding to volume levels within the bucket.)

    Something to weigh the LR sample.
    (Anything from a triple beam balance to a bathroom scale.)

    (1) Weigh the LR sample. Record the weight.
    (2) Fill the container to a known volume adequate to completely cover the LR sample (... but not so full that the displacement from the live rock will overflow the container.) Record this initial volume.
    (3) Place the LR sample in the container. Record the new volume.
    (4) Subtract the initial volume from the new volume. This is the displacement volume.
    (5) Divide the displacement volume by the weight of the LR sample. This is the volume of water displaced per unit weight.
    (6) Perform whatever conversions are required for convenience (if any).
    (7) Multiply the total weight of LR represented by the sample by the result of step (6). This is the estimate of the water displaced by all of the live rock (*).

    (*) If you have more than one variety of LR, repeat steps (1) - (7) with a sample representative of each variety and add the results to get the total displacement of all varieties of the LR.


    (step 1) LR sample weight: .25 pounds.
    (step 2) Initial Volume: 400 ml.
    (step 3) New Volume: 490 ml.
    (step 4) Displacement Volume = 490 - 400 = 90 ml.

    (step 5) 90 / .25 = 360 ml/pound

    (step 6) [ 1 Gallon / 3800 ml] times [360 ml/pound] = 0.09 Gallons/pound (*)
    (*) Or you could have just multilied 360 ml by 0.000264172 Gallons = 0.09 Gallons/pound

    Conversions Link:

    Someone else gave this link in a recent thread ... I use it all the time. HINT: To get the conversion number, simply enter 1 where the box says, "For The Number" and select whichever units you need.

    Finally ...
    (step 7) [150 pound] times [0.09 Gallons/pound] = 13.5 Gallons Total Displacement.

    This is an example only ... your numbers will be different, but the concept is the same. I have a similar procedure for guessimating the displacement for the DSB, but I think this is enough abuse to inflict upon you in one extended post.
    I used to inflict this stuff as a lab exercise on Physical/Earth Science HS students on a yearly basis. The percentage error was typically less than +/- 3%.

    I just love this kind of stuff ... unfortunately the doctors say the brain damage is probably permanent ... oh well.

    Remember, Bob's estimation guideline is really all you'll need. The original dosing levels (... and ZEOvit media volume/reactor flowrate ...) are volume dependent ... true enough ... but the artistry of the ZEOvit system requires dosing modifications in response to observations of the system's specimens.

    "When the going gets weird, the weird turn pro."
    Hunter S. Thompson


    • #3
      how much LR is "typical"?


      • #4
        Originally posted by jonah310
        how much LR is "typical"?

        I used a system similar to Meso.

        I took a bucket and made 1/4 gal marks on the side and took a few pieces of LR from the system representing different sizes. Then I looked at each rock in the system an assigned a value to it, then added that up.

        From now on I'll go with the 20% factor.

        “People are very open-minded about new things - as long as they're exactly like the old ones.”
        ...Charles F. Kettering


        • #5
          Greetings All !

          ... if you're adding the "typical" amount of LR to a tank.
          how much LR is "typical"?
          It depends on whose literature you read, when it was published, and the "style" you've selected for your system.

          If you're using the literature from Wilkens, Delbeek, Sprung, Moe, or Thiel ... Wilkens originally in 1970's followed by the others through early-mid 1990's ... you'll find suggestions in the 2 lbs. LR per 1 gallon empty tank volume range as being "typical".

          If you're using more contemporary literature, the "typical" ratio drops to 1 - 1.5 lbs. LR per 1 gallon empty tank volume. These ratios are presented by folks like Fenner, Calfo, and Borneman.

          Interestingly, the "required" ratio drops to zero with ZEOvit methodology.

          Last edited by mesocosm; 03-16-2005, 07:44 PM.
          "When the going gets weird, the weird turn pro."
          Hunter S. Thompson