Desired Salinity

I am looking for a salinity calculator that will tell me how much salt I need to add to my water change volume to bring it up to my target salinity. For example, if I am going to do a 5 gal w/c I have 5 gal of water in a bucket ready to go. I measure the salinity in the bucket and lets say it is 1.021 how much more salt do I need to add to bring it up to 1.025? Currently I add a little bit of salt stir measure, add more salt stir measure, add some water because I am too high then stir and measure. There has to be a better way.

I tried to search the forums but could not find any threads that deal with this scenario so if I missed something point me in the right direction.

Thanks.

 

Welcome to 3reef, I just do what you are doing, but simply measure how much I put in each time until I get to my preferred SG and then add that total to the suggested amount.

 

Use the formula:

(sg of added water * volume added) + (sg of tank water * (REAL tank volume - volume added) ) = (total salt level * total tank volume)

You're going to want to solve for sg of added water (as in, put X there), and plug in the rest with the variables you already have. Total salt level will be your target salt level. The rest should be obvious. Solve like you're back in high school doing algebra.

You need to know your real volume for this to work well. A 45g tank with 75# of rock will not have 45g of water volume, more like 25 or 30 depending on the density of the rock.

 

@blackraven
If I understand your formula correctly that would tell me what salinity I would need to add to the tank to get the correct desired salinity.

I just want to premix my 5 gal of water to 1.025. So I add some salt and measure and lets say my 5 gal of premix comes back as 1.021, how much salt do I add to bring my 5 gal of premix to 1.025?

I was looking for a formula or some online calculator that I could use to tell me this info instead of just keep adding salt and measuring until I am at my desired salinity.

 

Does the salt your using say how much per gallon to get to a certain sg? Not all salts are going to mix to the same sg so I would refer back to the salt bag/bucket.

 

I use the method you are using. It really is just trial and error until you get the formula down

 

Oh, for that, you just add a bit at a time and remeasure. In a 5g bucket, I think I saw about 2 1/2 cups of salt from tap to 1.025, so maybe 1/3rd cup till you see it change?

As you go along, you'll figure out exactly how much of a given salt mix you need per 5g to make your 1.025.

 

yeah like everyone else posted..also you could just mix up salt to 1.025 and then just add some of that to your top off..it will slowly add more salt to your tank..either way you do it you want to do it very slowly, so the evaporation way is the best..also you need to mark somewhere on your tank where the water should be always, so that you can keep a stable SG, unless you have an auto top off..but the formula in the first reply is what i use..but its kinda a guessing game knowing exactly how much water volume you have, so i just use the evaporation top off with a little higher salinity if i ever had a problem with salt too low..also you wanna make sure you dont have alot of bubbles in your tank that will cause salt creep, salt creep will alter you salinity very easily too..

 

i use coralife salt and for about 5 gallons of water it takes me around 5cups to get 1.025.5-1.026..

also you need to have the temp of the freshwater the same as the tank, because temp affects the salinity of the water..

 

Well dang...I was hoping for some sort of formula or calculator that would tell me to add x amount of pounds/ounces of salt.

Just as an FYI, I am using Instant Ocean Reef Crystals.