how do i calculate a change in salinity?

[jedheuer]

For example:

If I have a volume of 140 gallons at specific gravity 1.026 or 35 ppt and I add 20 gallons of pure RODI water what will the resulting specific gravity be? how is this figured?

Thanks!

 

[Randy Holmes-Farley]

The 35 ppt part is easy: it is just proportional.

So the final salinity would be:

[140 x (35) + 20 x (0)]/(140+20) = 30.6 ppt

Using sg, you can just drop the leading 1.0, so:

[140 x (26) + 20 x (0)]/(140+20) = 22.75 ---> 1.02275

 

[jedheuer]

Thanks. I knew it must be simple but numbers are never simple for me! this is clear though so thanks again.

 

[Randy Holmes-Farley]

:thumbsup:

Happy Reefing.

 

[jedheuer]

While we are at it do you think this is a 'safe' drop in salinity? I am calculating a worst case scenario if my 20 gallon reservoir were to add all its contents to the tank at once. Would I see a serious die off at this low salinity? I am planning some fail safes but I am concerned about a worst case scenario.

 

[Randy Holmes-Farley]

How fast? Instantly?

1 (maybe 2) ppt might be the largest instant drop I'd want in an emergency if it could be prevented. Over an hour, a few ppt might be OK.

 

[jedheuer]

I am using aqualifter for top off which is rated at 3 1/2 gallons per hour. also I might put a timer on the ATO as well in order to minimize the risk and increase the chance of me catching the ATO stuck on.

 

[Randy Holmes-Farley]

Sounds like a good plan.

Home Depot now sells cheap electronic times that can have 20 on/off per day, as long or short as you want (1 minute minimum), which might work well here.

 

[jedheuer]

Sounds like a good plan.

Home Depot now sells cheap electronic times that can have 20 on/off per day, as long or short as you want (1 minute minimum), which might work well here.

Yes, I have a few of these type, they work well.

Thanks again!

 

[Randy Holmes-Farley]

:thumbsup:

Good luck.