# Measuring Aquarium Salt

#### ap4lmtree

##### Well Known
Member
I have a freshwater aquarium; however, I am asking here because you guys know more about aquarium salt and salinity.

For my freshwater aquarium, if I put 6 teaspoons of aquarium salt for a 10 gallon aquarium. Then, if in two days I change 1/3 of the water, would adding 2 teaspoons of salt at that time give me the same or close to the same salt concentration as I had in the beginning, 6 tsp of salt per 10 gallon?

##### Well Known
Member
Here’s a quick equation....

Concentration = c
Volume= v

C1 x V 1 = C2 x V2

OP

#### ap4lmtree

##### Well Known
Member
Yes, I realize that, but I am wondering if when I put 6 tsp of aquarium salt, does it eventually get eventually distributed throughout the aquarium rather than a possibly of it going to just one location, such as at the bottom. Does the salt combine with water to become one chemical throughout the water or is it remotely possible that it congregates to certain regions of the aquarium.

##### Well Known
Member
it will dissolve in the water, so long as there isn't so much of a concentration that it will be saturated (think about hot chocolate mixes in water lol)

so your question is about solubility instead of concentration... got it. solubility is dependant on many physical factors but I imagine it would be extremely expensive to actually create a saturated mixture in a tank so large, yeah?
what are you planning on doing? just curious?

OP

#### ap4lmtree

##### Well Known
Member
I am not trying to do anything too technical. I simply want to maintain ~.8 tsp of aquarium salt per gallon after doing a 50% or so water change for my tanks. I was just wondering if by having the salt dissipate in the water, that it gets evenly spread and that adding more aquarium salt would keep the total aquarium water concentration the same.

#### stella1979

##### Moderator
Moderator
Member
Yes, if you're not trying to be extremely precise, the same measurement of salt will get you the same concentration in your aquarium water. I know this because I weigh (to the gram) marine salt every week, add it to the 4 gallons I've gathered for a salty aquarium's water change, then do that water change... really knowing all is well by the happiness of sensitive corals. However, I also measure the salinity of both the tank and prepped water with a calibrated refractometer. This has been working out for me for 2 years, there is no variation in salinity in my tank, (read below) and there has been no variation in the amount of salt needed per gallon.

What it doesn't appear you are accounting for is evaporation. Saltwater tanks get topped off at least once a day to counteract (what would be) rises in salinity due to evaporation. My 20-gallon reef tank (with a fairly tight-fitting glass lid) can evaporate up to 32 ounces of water every day... This is quite a lot and the critters I have inside are happier with an automatic top off unit (ATO) than they were in the early days (without an ATO) when we were manually topping off once per day... meaning, the ATO maintains with small top offs multiple times daily, leading to less variation. However... I'm not suggesting that you need an ATO, I'm just saying that you'll want to watch your water line very closely to avoid major swings... and believe it or not, the salinity in smaller tanks swings faster due to evap than it does in larger tanks. Without getting technical, just consider surface area to overall volume. Anyway, just find a spot to mark your waterline fairly precisely. Every morning and evening, add fresh water to maintain that line.

Hope this helps!