Formula for lowering salinity

[rudedog40]

Ok. So i need to QT this tang with ich. The hypo treatment says to lower the SG to 1.009 over the course of 48 hours. Is there a magical formula that tells you how many gallons to pull out of a tank and replace with fresh RO water to do this gradual decrease in salinity? Meaning, I have a 20g QT with a current SG of 1.026. How many gallons of water do I replace to get the SG to 1.0175 (halfway between 1.026 and 1.009) the first 24 hours? Once I have it to 1.0175, how many more gallons to get it to 1.009 24 hours after that?

 

[earlybird]

I though there was one also. I just used a red dixie cup and replaced a cup of tank water with a cup of RO. As the salinity gets lower you'll need a lot more to drop it down. I just kept rechecking it often. Pretty easy, you'll see.

 

[dinogeorge]

Earlybird has a good method.
I would also suggest the following:
1) Take your SG reading with your refractometer.
2) Using a standard measuring cup remove one cup of water from your tank.
3) Replace that cup of saltwater with your fresh RO water.
4) Let that water mix well in your tank.
5) Take a new reading of your tank with your refractometer.
6) Make note of the amount of SG reduction that one cup had on your overall SG.
Now that you know how much one cup of water impacts your tanks overall SG, you can calculate how many cups of water you will need to reduce your SG to .09. Then, divide that amount by 48 hours and that will give you a general idea of how many cups per day you will need to remove and replace.
But keep in mind that this is by no means absolute. There are several factors that will come into play. You MUST constantly monitor your SG. Each cup of water you remove will have less and less salt in it, and therfore you will need more cups than your original calculations. But, this gives you much better idea of what you need to do.

 

[renogaw]

when i lowered my SG for my recent ich battle, i went by directions i could find on a different website:
Your starting point should be between 1.025 and 1.027. Replace about one fifth of the volume with RO, RO/DI or aged freshwater that has been well aerated. Repeat this 12, 24 and 36 hours later, monitoring the specific gravity along the way. After the fourth water change the specific gravity should be 1.010 or pretty close. Wait a few hours to make the final adjustment to get down to 1.009.

my fish did not get stressed (as far as i can tell, although the royal gramma eventually died from fin rot). it was harder to get from 1.010 to 1.009 than it was to get down from any other level.

 

[earlybird]

Originally Posted by renogaw
when i lowered my SG for my recent ich battle, i went by directions i could find on a different website:
my fish did not get stressed (as far as i can tell, although the royal gramma eventually died from fin rot). it was harder to get from 1.010 to 1.009 than it was to get down from any other level.
I saw the same thing but wanted to make it more gradual and I had the time. I actually took off 2 days from work to babysit my tank. It turned into a long weekend.