Where does the salt go in a water change


New member
This may be a silly question to many but I am curious about adding salt when doing a water change. When I do a top off, we never add salt to the water, just simply pour RO water into the sump. Top off is normally around a gallon or so. It's a 90 gallon tank. However, when I do a water change (first one coming this weekend) I am suppose to set aside the fresh RO water in a container, make sure it is right temperature and add the right amount of salt for the gallons I am putting into the tank. When you siphon out water, does it take a lot of the salt with it? Just curious the thinking behind this and please don't laugh at me for the question :)


New member
Yup it is a "saltwater" tank. =)..

What your replacing daily is water that is evaporating from the tank. The salt does not evaporate and stays in the water making the salinity (salt content) higher.

A water change is taking a certain amount of salt water out and replacing it. Still making sure you added the freshwater that day if needed before changing the mixed water. (if that makes sense =)

Using a refractometer will tell you how much salt is in your tank and also freshly mixed water.


Team RC member
Team RC
Yes, you're removing salt with the water.

What she said. Saltwater, once the salt is dissolved, is homogeneous which means that each gallon is of identical content from a dissolved solids perspective (which includes salt).


New member
That helps clear it up. I just wanted to be sure before I do the water change so that my salinity isn't too high and hurt/kill what I already have.


New member
If it's possible mix your sw the night before you put it in, use a power head if you have one. It gives it a chance to fully dissolve


Staff member
RC Mod
Also read the label of your salt mix: there's a lot more than NaCL in there (salt). There's boron, calcium, selenium, etc, etc---in correct proportions. Think of it as dehydrated seawater.

(When I get a new monster tub of salt, and use a little, I lay the thing on its side and roll it a bit to be sure it hasn't layered itself in the vibration of shipping. I don't know that it does a thing. But I did have a barrel come in that seemed a little powdery on top.)


New member
I have a brand new white Rural King Feed Bucket that is 20 gallons. It does not say that it is "food grade" but I would like to use it to store my mixed saltwater the day before I do a water change. I have only used the bucket once to transport RO water when I was setting up my tank so there was nothing in it. Do I have anything to worry about using it?