Formula for salinity correction

[Oregon Grown Reef]

Have you ever tested your tank salinity and found it to be too high or too low? I know I have. I hated guessing what salinity water I had to use to increase or decrease my salinity to the desired level. Well guess no longer, friend. I'm sure this formula is used for other things, but I figured it out with the help of my beautiful wife and some deduction so I wouldn't have to guess anymore. I've tested it many times and it always gives the correct answer. For the sake of not putting out the longest read in Reef2Reef history, I won't include changing from a lower salinity to a higher salinity, but rest assured it works.

***Keep in mind, when adjusting salinity, all other major/minor/trace elements will be rise/fall depending on the direction you go. This is used solely for the purpose of changing the salinity.***

Here it is:

((A(t-r)+(t-R)C)/t=D

A=Current Tank Salinity
C=New Water Salinity
t=Total aquarium volume
r=Removed volume of water
R=Remaining volume of water
D-Desired Salinity
(edited)

Here's are some examples of it working.

Say you have a 80 gallon tank, the salinity is sky high at 1.030, and you're wanting to do a water change to correct it. You choose the desired amount of water you want to change, use this formula, and you'll never have to guess. For this example, we'll change out 10 gallons of water and target a salinity of 1.026. You'll just use the order of operations and voila. In this instance, when you're changing out water, you're solving for "C".

((1.030(80-10)+(80-70)C)/80=1.026

((72.1+10C)/80=1.026

72.1+10C=82.08

10C=9.98

C=.998

Now we'll plug it in to make sure it works. You'll use the 2nd step in the formula to answer for confirmation. This just stops you from having to redo math.

(72.1+10x.998)/80=1.026

82.08/80=1.026

1.026=1.026

BUT WAIT, THERE'S MORE. You can also use it to determine how much saltwater to remove and replace with RODI water at 0 salinity. You don't have to change out the water if you don't want to. In this example, we're solving for "r".

((1.030(80-r)+(80-R)0)/80=1.026

(1.030(80-r))/80=1.026

(82.4-1.030r)/80=1.026

82.4-1.030r=82.08

-1.030r=-0.032

r=0.31067961165048543689320388349515

Now only for the sake of the equation am I copying the entire answer. You don't need to be so accurate when you're adding the water.

Now we plug in the number we got for "r" into our original formula for adding RODI.

((1.030(80-0.31067961165048543689320388349515)+(80-R)0)/80=1.026

((1.030*79.689320388349514563106796116505)/80=1.026

82.08/80=1.026

1.026=1.026

TL;DR- The formula works. I just wanted to show you that it worked. No more guessing, no more over/under adjusting. Good luck and happy reefing!

 

[JosephM]

Love me some math but I’m lazy lol

Target Salinity Calculator

Aquarium calculator; Create a water-change schedule that can be used to reach a target salinity.

www.hamzasreef.com

Direct Salt Addition Calculator

Aquarium calculator; Estimate the amount of solid salt required to raise salinity to a target level.

www.hamzasreef.com

 

[laverda]

That's great! Only thing if your salinity got as far off as you examples I would not correct in one water change. Most salinity changes happen gradualy over time. Our fish and corals adjust to them up to a point. Correcting them too quickly can actually be worse for them.

 

[JosephM]

That's great! Only thing if your salinity got as far off as you examples I would not correct in one water change. Most salinity changes happen gradualy over time. Our fish and corals adjust to them up to a point. Correcting them too quickly can actually be worse for them.

Oh yeah 100%, learned that the hard way after adding salt directly to tank

The first link is really helpful for water changes when you want to slowly raise the salinity over a couple water changes.

 

[Oregon Grown Reef]

Love me some math but I’m lazy lol

Target Salinity Calculator

Aquarium calculator; Create a water-change schedule that can be used to reach a target salinity.

www.hamzasreef.com

Direct Salt Addition Calculator

Aquarium calculator; Estimate the amount of solid salt required to raise salinity to a target level.

www.hamzasreef.com

Those work well if you're wanting to choose the amount of water changed, but this formula tells you exactly how much water is needed to change it without picking an arbitrary number. Here's a screenshot for example. I choose 5 gallons as a water change amount and it's recommending 3 water changes of 5 gallons each to reach the desired level.

Edit: To clarify, you still have to choose the amount of water if you're raising the salinity in the equation or using water changes to lower it. It does however tell you exactly how much RODI is needed to lower it if you're not doing a water change. This comes in handy especially when you're using the balling method.

 

[JosephM]

Those work well if you're wanting to choose the amount of water changed, but this formula tells you exactly how much water is needed to change it without picking an arbitrary number. Here's a screenshot for example. I choose 5 gallons as a water change amount and it's recommending 3 water changes of 5 gallons each to reach the desired level.

Looks like I’m switching over
That’s a really neat feature. Thank goodness my salinity doesn’t drop too much or too fast. Unless I get a big package of corals in and have to take water out with rinsing and such

 

[Oregon Grown Reef]

That's great! Only thing if your salinity got as far off as you examples I would not correct in one water change. Most salinity changes happen gradualy over time. Our fish and corals adjust to them up to a point. Correcting them too quickly can actually be worse for them.

Which is why you can choose a specific amount you're wanting to adjust it to. I guess I just never used the hamza's reef calculators. It seems like it's probably using the same formula, but only suggesting it in smaller increments.

 

[Oregon Grown Reef]

That's great! Only thing if your salinity got as far off as you examples I would not correct in one water change. Most salinity changes happen gradualy over time. Our fish and corals adjust to them up to a point. Correcting them too quickly can actually be worse for them.

I'd also hope one would be checking their salinity more regularly so they wouldn't be making large changes too.

 

[Oregon Grown Reef]

I think the biggest, if not the only, advantage this formula has is if you're at a salinity of 1.027 and want to drop down to 1.026. That's easily doable in 1 go. You have to start choosing numbers randomly until it says change x amount at 0 specific gravity.

 

[Oregon Grown Reef]

I think the biggest, if not the only, advantage this formula has is if you're at a salinity of 1.027 and want to drop down to 1.026. That's easily doable in 1 go. You have to start choosing numbers randomly until it says change x amount at 0 specific gravity.

And even then, it may only be a portion of a gallon depending on tank size.

 

[Oregon Grown Reef]

#MODS, for some reason my last edit didn't take. The legend is incorrect. B should be "C" and C should be "D".

 

[Val Shebeko]

You can lead reef keepers to water but......

 

[Randy Holmes-Farley]

#MODS, for some reason my last edit didn't take. The legend is incorrect. B should be "C" and C should be "D".

Can you clarify exactly what you want changed where? I'll make whatever changes are needed.

 

[Oregon Grown Reef]

Can you clarify exactly what you want changed where? I'll make whatever changes are needed.

Yeah. It's the key right below the formula. You can just copy and paste this.

A=Current Tank Salinity
C=New Water Salinity
t=Total aquarium volume
r=Removed volume of water
R=Remaining volume of water
D-Desired Salinity

Thank you!

 

[Randy Holmes-Farley]

That do it?

 

[Oregon Grown Reef]

That do it?

Yes. Thank you, sir.