Calculating Salinity

patrikk

New member
Hi,

I wonder if someonce could be kind enough to tell me the formula for adjusting salinity with only adding water(for reduction) or salt(for increase).

I would also like to know the formula for adjusting salinity when doing water changes. I know it depends of the type of salt but the formula could use the vairable X for the salt dosing etc.


Thank you for the help and a great forum with helpful and great reefers.


//Patrik
 

Truck54

In Memoriam
Salt

Salt

If you want to raise it, take some water out,add more salt to it, mix and put it back in your tank. If you want to lower it, take some salt water out of the tank, and add some fresh water.
 

Kingspade18

New member
mine is at like 35-36pp is that too high? i only have a few fish and a zoo colony right now and all seem to be thriving so far but its only been a week. wouldnt dropping it a couple points in a single dose shock the inhabitants?
 

EllieSuz

Premium Member
The method you use to measure salinity is very important. If you don't have a refractometer, you should get one. I wish there was a recipe for mixing salt, but there isn't. There are too many variables to consider. You just have to add salt if needed or add RO/DI water as needed. For instance, I've learned that it takes a heaping half cup per gallon of Instant Ocean to get me close to the specific gravity I want and then I tweak it until it's right on. Another thing a lot of newbies aren't aware of is that the water temperature affects salinity. When you mix new saltwater be sure to keep a small pump and heater in the mixing container.
 

Jarmen

New member
It may not be necessary to heat your salt water just for the purposes of checking salinity using a hydrometer. The change in the density of water at temperatures that we would encounter in this hobby should be negligible. Specifically according to Randy's article on SG, the density change between salt water (s=35) at 60°f and 77°f is .0005.

How big of a salinity change are you trying to make? You should be able to get an idea of what you are going to have to do by using a weighted average.

Jason
 
Last edited:

Blayz77

New member
i dont heat my water when mixing it. i just put 5 gallons of ro/di water in a bucket, doesnt really matter the salt mix you use most often it will say use half cup per gallon. so i measure out 5 lvl half cups toss em in bucket and let a pump mix it up for a few hours. after that i will check the salinity with a refractometer and adjust if needed. for me its usually right on or very close. if it needs to be adjusted i only have to add a few pinches of salt of a splash of ro water.

.35 is about the most you want to be at 1.024 - 1.027 is the optimal range i think.
 

bertoni

Premium Member
For small changes, SG is close enough to linear for our purposes. So to dilute water at 1.027 SG down to 1.026 G, add roughly 1/27 of the total tank volume in RO/DI water. So that's about 3.7 g for a tank with 100 g total in water volume. Adding salt to increase the SG is a much harder question, because salt products vary in their water content, and thus are harder to measure.

I would increase the SG of a system by topping off with saltwater, anyway, as it's gentler and safer. To reduce the SG, I just pulled a bit of water out each day, and let the ATO slowly replace it.
 

Mavrk

New member
I would increase the SG of a system by topping off with saltwater, anyway, as it's gentler and safer. To reduce the SG, I just pulled a bit of water out each day, and let the ATO slowly replace it.

This is the best advice and well stated.
 

tmz

ReefKeeping Mag staff
Premium Member
The linear count Jonathan noted is easiest for going down. This is from my notes as a example:


For 100gallons at 1.030

ro/di to replace 1.030:
2 gallons = 1.0294
4gallons=1.0288
6gallons=1.0282
etc.

I agree going up via top of is the safe way and easy for an active tank. If you are mixing a batch and want to raise it. This may help:

I know this could be more elegant but it's the best I can do( maybe a math guy will chime in);hope it its helpful:

raising sg from 1.025 to 1.026 with a ten % water change. Other values can be substituted.

.9 x .025 =.0225 then .0225 + .1 x n= .026
.1x n =.026 -.0225
.1 x n = .0035
n= .035
So for a bump from 1.025 to 1.026 ,replacing 10% of the 1.025 water volume with 1.035 water is needed. I think that's the right math.
 

eagle9252

New member
All of that stuff is hard for some people to understand.

Simple.

Take a gallon jug with 1 gallon of water measured. You will find that it stops about 2 in from the top. Depending on the salt your using you will have to play with it.

IO and RC was like 1/2cup plus 1 tbs to get 1.026sg so I was loosely putting in about 8cups per 15 gallons

Red Sea Coral pro. I use 7cups per 15g that's about .46cup per gallon

And salinity which I just bought another bucket full to change back to was about 3/8 cup per gallon.
So I will use 5-5/8 cup per 15 gallons.

I actually toured the Seachem plant last week and it was awesome.

I have used a couple of different brands. I personally like the Salinity from Seachem. I started with RC and got a deal on some Salinity and used 2 buckets of it and then got a smoking deal on IO the first of this year but I don't like or want to dose. There was a lot of talk about the new Red Sea Coral Pro coming out so I got 2 buckets. I've used 1 ½ so far and think I'm going to switch back to Salinity as the levels are about the same but you use less for each batch.
 

Blayz77

New member
ive used my top off before to raise salinity before it works good. ive even done water changes using it heh. its a lot slower but i would put a drip line into an empty bucket and let my top off add new saltwater until the 5 gallons were gone. its much easier to just check the salinity of the new saltwater before adding and make ajustments accordingly
 

patrikk

New member
The linear count Jonathan noted is easiest for going down. This is from my notes as a example:


For 100gallons at 1.030

ro/di to replace 1.030:
2 gallons = 1.0294
4gallons=1.0288
6gallons=1.0282
etc.

I agree going up via top of is the safe way and easy for an active tank. If you are mixing a batch and want to raise it. This may help:

I know this could be more elegant but it's the best I can do( maybe a math guy will chime in);hope it its helpful:

raising sg from 1.025 to 1.026 with a ten % water change. Other values can be substituted.

.9 x .025 =.0225 then .0225 + .1 x n= .026
.1x n =.026 -.0225
.1 x n = .0035
n= .035
So for a bump from 1.025 to 1.026 ,replacing 10% of the 1.025 water volume with 1.035 water is needed. I think that's the right math.

Thank you Tom this is just what I was looking for. it was very straight forward I thought it would be more complicated, Im almost ashamed that I had to ask :)

Well now that my self-esteem is low I might as well ask another question ( it's past midnight here now so I can always blame my stupid question on that )

Could any tell me how to obtain 1.035 salinity from any salt say e.g. Red Sea Coral Pro. The instructions only explain "normal" salinity mixing ( 1.021 - 1.025).

I guess its the same for all brands and how to calculate it depends on the dosing. But could someone please explain it ?

I thought it would be as simple as say:
from the bucket info:
1.021 requires 33.4 g /litre
1.023 requires 36.0 g /litre
1.025 requires 38.2 g /litre

so now I thought just take 33.4 divided by 21 and you get gram / salinity point (0.001)
So I tried 33.4 / 21 = 1.59047619

so I make a reference calculation to obtain 1.025:
1.59047619* 25 =39.7619048

and on the bucket it says 38.2

Please help me out with this one as well.

And thanks again for the help before ( I appreciated all replies, however Tom had he answer I needed so thanks again).
 

eagle9252

New member
WELL...

I was going to answer your question with a see my answer as it would still be the same.
Take the time that you are waiting for someone to answer your question and figure it out yourself but then I remember I just bumped my WC mix up because I decided to change 20 gallons instead of 15 but mixing station only holds 15 so I added 3 cups more. I just check the SG and its 1.034. I used 10 cups of RSCP
 

tmz

ReefKeeping Mag staff
Premium Member
Thank you Tom this is just what I was looking for. it was very straight forward I thought it would be more complicated, Im almost ashamed that I had to ask :)

Well now that my self-esteem is low I might as well ask another question ( it's past midnight here now so I can always blame my stupid question on that )

Could any tell me how to obtain 1.035 salinity from any salt say e.g. Red Sea Coral Pro. The instructions only explain "normal" salinity mixing ( 1.021 - 1.025).

I guess its the same for all brands and how to calculate it depends on the dosing. But could someone please explain it ?

I thought it would be as simple as say:
from the bucket info:
1.021 requires 33.4 g /litre
1.023 requires 36.0 g /litre
1.025 requires 38.2 g /litre

so now I thought just take 33.4 divided by 21 and you get gram / salinity point (0.001)
So I tried 33.4 / 21 = 1.59047619

so I make a reference calculation to obtain 1.025:
1.59047619* 25 =39.7619048

and on the bucket it says 38.2

Please help me out with this one as well.

And thanks again for the help before ( I appreciated all replies, however Tom had he answer I needed so thanks again).

You are welcome.
I sitll hope someone checks it. I do use it for upping sg in transfer quarantine tanks to up the sg, along the way toward getting fish acclimated to the main system sg. Since these are transfer tanks each has newly mixed salt water and top of corections don't fit this aplication. I check with a conductivity meter and refractometer and the calculation it seems to work ok.

The second question is different since it involves the salt mix itself not premixed salt water which I used in my calculation to get around that variable. The dry mix is probably not completely anhydrous (ie it has water in) This would make a linear calculation for sg or salinity without an accounting of the water in the mix inaccurate. Seems to get pretty complicated.

I tried it this way : 23 divided by 21 = 1.095 x 33.4g =36.58,so that's off by .58 fro the bucket measure and then 25 divided by 21 =1.19047 x 33.4g=39.7619; so, that's off by 1.56 grams from the bucket measure. Don't know how to figure the water content of the dry mix from that though.
 
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