Calculating actual volume of water in tank

[jamal-188]

I was wondering today if everybody calculates the "actual" amount of water in there tank. By this I mean if you have a 100g tank, obvisously there is not 100g due to all the room sand/rock/etc take up. So, if you're doing a 20% water change, will you swap out 20gallons or a bit less figuring that 20% of the actual water may only be 15 gallons.

The same goes for dosing medication. If the directions say use 1 tablespoon for each 5 gallons, I"m assuming they mean the "actual" amount of water in the tank.

Anybody know of a rough way to calculate this, I swear there was a calculator somewhere but I cannot seem to find it

 

[sw-addict]

Morning jamal-188 it must be early for you the calculaors are at the top of the pages in the little bars it says calc just go up ^ to the top.
I looked everywhere for it too.

have a good one

 

[fishfreek]

I have not seen a calculator that will give you a water volume after displacment. Personally if I do a 20% water change I change out the amount based on zero displacement.

One thing thats hard to do is govern the amount that a rock of a given weight will displace. Since rocks have different dentisty a very dense rock will displace less than a very porus rock. SHOOT I have even see live rocks that are so porus they end up floating or having near nutral boyancy.

 

[yaksplat]

If you want to get relatively close, assume 10-15 lb/gallon for rock. You can also assume 8# for every 144 cubic inches of sand, or .6 gallons

so, if you have a 55 gallon tank with 3 inches of sand and 150# of rock, you can estimate that you have:

55gal - 7.2 gal (sand) - 10 gal (rock) = 37.8 gallons of saltwater.

This is just a rough estimate, but it will get you in the right ballpark.

Jim

 

[MiniReef2004]

I found a calc at www.garf.org that will give you a good estimate. HTH

Steve & Dee

 

[yaksplat]

not bad, i was only off by about 3 gallons