How Much Water is REALLY in There?

[jumpfrog]

We always talk about the number of gallons in our tanks so I got to thinking, just how much water is really in there?
Here's my train of though........any comments?
Start with my 125 predrilled. Taking the true measurements and calculating volume you're down to 123.4 gallons.
Given there are overflows the water is already about an inch down from the top measurement, now I'm down to 117.8 gallons (not smart enough to figure out how much volume is lost in the overflows themselves so for this exercise I'll just ignore the loss)
I have a 3" sand bed so now I'm down 101 gallons.
When I do a 16 gallon water change my water level drops 4 inches.
So 22" height minus 1" for overflows height minus 3" for sand leaves me 18 inches. If 16 gallons equals 4" of water that each inch would equal 4 gallons.
My 18" of tank room now drops me to 72 gallons.
My beautiful 125 now only holds 72 gallons :scared:

 

[georgene]

You lost 52 g of water. Makes me think how much I have lost in my 72 g. We all have something to think about when adding meds.

 

[moneyman]

72 * 18 * 18 = 23,328 in^3. Thats 101 liquid US gallon.
... dont forget your LR.

 

[dejaco]

Okay 210 gallon system - with 45 gallon tank for sump.
3 - 4 inch layer of sand, 280 lbs live rock, and pumps taking up room in sump (which is only half full), and to fill entire system takes 192 gallons of water.
We carted it in by 5 and 1 gallon containers. Yes that all we lost for displacement.

 

[jumpfrog]

Any other thoughts

 

[dmm0724]

sounds like you are some kind of math fanatic.....
i just try not to think that deeply...seems to help me :hilarious

 

[jumpfrog]

If you only knew how much I suck at math!
The whole point of the thread was to get some feedback on my train of thought.
So many decisions are made on water volume in regards to dosing and water flow, turn over etc. If we make our decision based on the most water a tank can hold vs. the actual amount of water in the tank, we would have two very different answers. :notsure:

 

[oceana]

Originally Posted by georgene
You lost 52 g of water. Makes me think how much I have lost in my 72 g. We all have something to think about when adding meds.

they think of that for you. most company take into account an AVERAGE when saying how much to put in your water.

 

[jds31788]

easiest way would be to fill up the tank and then add all ur stuff(rock sand whatever) and measure the displacement because the rock hold water inside them and the sand isnt a solid 3 inches. IMO its a little impractical to be that precise but its your railroad. hope u guys dont hurt urslefs with all this computing lol

 

[hagfish]

I wouldn't worry much about this. If your dosing, I would always err on the side of being conservative (I don't dose anything, salt has most of what I need). For flow, more is generally better in almost all cases with a reef. Unless you have softies that can't hold on anymore. The inches of fish per gallon rule may be affected a little with this I suppose. Again, it's probably best to be conservative with how many fish are put in anyway.

 

[relaxn79]

ya it's true. I had a brand new 40g tank with 36 gallons of water. After adding 50lbs of sand I still had left over water. I figure there is about 32 gallons of water in my 40 gallon tank.