Newbie ? on water displacement

[MaximaPower]

me and my lil bro had a discussion on water displacement because he says my stand isn't strong enough for all the LR and sand + the water....well i told him the tank will always weigh the same.(if the tanks is filled all the way up w/water)

so am I right? a 75 gallon tank filled up with just water will weigh the same as a 75 gallon tank with 200lbs of LR & sand with water filled up.

I'm hoping that i'm right, cus the stand i have doesn't look to sturdy...but it held up perfectly fine when i did freshwater

~Nam

[minimasterflash]

The short anwser is, if your stand can safely (safely is a key word) support a tank full of water, then adding sand and liverock shouldn't stress the stand much more.

The long anwser is adding sand and rock does increase the weight of a tank full of water. Assuming of course that your rock and sand doesn't float or become neutrally boyant. Average rock density is in the 2.25-3.25 g/cc range (water is 1g/cc). I would imagine sand to be in that general range also, given a small grain size. If you add anything that sinks to a tank of water the total weight is increased, if it floats you decrease the total weight.

These are rough calcs, but should represent the differences

75gal water only = 625lbs

75 gallon tank with 200lbs of rock/sand filled with water = 745lbs

If you would like to see more detail calcs on how to do this i can provide.

-Yancey

p.s. I do know that figi is porous, but you have to assume that water completely fills the voids within.

[MaximaPower]

thanks for ur reply Yancey.

well i bought a stand for the 75 gal tank, but it looks very weak....it held up perfectly fine when i had a freshwater setup with just gravel and water, but i'm afraid it won't hold a reeftank....should i be worried? or are these stands really stronger than what they look like

[witecap4u]

If you doubt it, then throw a couple 2x4's in for support, at least one at each corner, and I would think you should be set for life....You can never be too safe...cs

[Andrew]

"you can never be too safe . . ." ;)

my 40 gal stand weighs at least 75 pounds

I think i have 3 two by fours per leg.