Science/Chemistry question:

Wayne Sallee wrote:
I don't think so.

Assuming: "1/2 cup of salt per gallon of salt water rule of thumb".

Assuming: 30 gallons of salt water made up to regular strength using the
"1/2 cup rule" as being the standard for the test.

Assuming: 30 gallons of regular strength water having to be taken out
for a standard water change.

Assuming: a tank size of 60 gallons.

Now for the test tank Assumptions ###########

Assuming: 5 gallons of evaporation.

Assuming: 27.5 gallons of extra salty water taken out of the tank. After
evaporation, your tank now holds 55 gallons of water, and a 50% water
change is 27.5 gallons. This 27.5 gallons of strong water is equivalent
to 30 gallons of normal strength water.


There in lies the flaw in your logic. One would not be taking out 27.5 -
one would still be taking out 30.

Therefore, one would be removing more phosphate, nitrate, etc.

Add Homonym wrote:

And Kurt is right, in this case. You WILL be removing more pollutants if
you do it this way (or alternately using less salt, if compared to what
you'd get if you top off first and remove enough water to take out the
same pollutants as if you removed water before you topped off)

I always prefer to plug in some numbers as an example. Let's say that I have a
100 liter tank (actual water capacity), my nitrate level is 30 mg/l, and I
decide to make a 25 liter water change. My SG is pretty high and water level is
down to 95 liters, so I actually only have to drain 20 liters. That removes 600
mg of nitrates. There is now 2250 mg of nitrates remaining in the tank. After
adding 25 liters of new water, the nitrate level will be 22.5 mg/l.

Now. Say I top off the water level first. I've diluted the nitrates, so my
nitrate level is now 28.5 mg/l. Draining 25 liters will remove 712.5 mg of
nitrates, leaving 2137.5 mg of nitrates in the tank. After adding the new water,
the nitrate level will be 21.375 mg/l.

George Patterson
If you torture the data long enough, eventually it will confess
to anything.

Did you read everything, or did you stop reading at
this point?

Wayne Sallee
Wayne's Pets


Add Homonym wrote on 3/15/2007 9:01 AM:
Wayne Sallee wrote:
I don't think so.

Assuming: "1/2 cup of salt per gallon of salt water rule of thumb".

Assuming: 30 gallons of salt water made up to regular strength using
the "1/2 cup rule" as being the standard for the test.

Assuming: 30 gallons of regular strength water having to be taken out
for a standard water change.

Assuming: a tank size of 60 gallons.

Now for the test tank Assumptions ###########

Assuming: 5 gallons of evaporation.

Assuming: 27.5 gallons of extra salty water taken out of the tank.
After evaporation, your tank now holds 55 gallons of water, and a 50%
water change is 27.5 gallons. This 27.5 gallons of strong water is
equivalent to 30 gallons of normal strength water.


There in lies the flaw in your logic. One would not be taking out 27.5 -
one would still be taking out 30.

Therefore, one would be removing more phosphate, nitrate, etc.