Salinity forumla needed

Steve1500 · Aug 14, 2019

Every once in a while I have to raise or lower the salinity of my DT. It is a 200G total volume system. Is there a calculator or formula to tell me what my salinity needs to be for a specific amount of water?

For example, for a 200G DT, the SG is at 1.024 and I want to bring it up to 1.025 with a 20G water change. What is the SG of the 20G that is needed to bring it to 1.025?

On the reverse, if I want to go from 1.026 to 1.025 on the same system with a 20G WC, what is the SG of the 20G needed to lower it to 1.025?

I have tried winging it, but I end up adding RODI to the DT to lower or sometimes adding salt (small amounts) directly to the DT to raise the SG. I know there are calculators out there to tell you how much salt to add DIRECTLY to your DT, but I don't want to do that. I would rather do a WC where the salt gases have dissipated.

Thanks

P-Dub · Aug 14, 2019

If you find this magic formula I want to know. In the meantime, to adjust my salinity up I just place a jar filled with salt in the sump in a low flow area and let it dissolve slowly and keep adding till I reach my target. I've yet to have to add just plain RO/DI to bring salinity down as my protein skimmer and ATO work to always lower my SG.

Beonedge · Aug 14, 2019

From : 200 g x 1.024 + 20g x Y = 220g x 1.025 /// Y=(220x1.025-200x1.024)/20 /// Y=1.035

... and then drain 20G

Steve1500 · Aug 14, 2019

Beonedge said:
From : 200 g x 1.024 + 20g x Y = 220g x 1.025 /// Y=(220x1.025-200x1.024)/20 /// Y=1.035 ... and then drain 20G

Wouldn’t Y (the SG of 20G) need to be greater than 1.024 in order to raise SG?

Peace River · Aug 14, 2019

Here is an R2R link that you may find helpful.

Here is a target salinity calculator.

Peace River · Aug 14, 2019

Steve1500 said:
Wouldn’t Y (the SG of 20G) need to be greater than 1.024 in order to raise SG?

Yes, in line with what @Beonedge calculated, the sg of the added 20g is 1.035 which is above 1.024. Although this is mathematically correct, I would suggest that you top of with your regular mix of saltwater (or maybe 1.027 or even 1.028) instead of RO until it raised to the desired level of 1.026 to maintain stability in your tank.

Ebslinger · Aug 14, 2019

Remember, evaporation is your friend when it comes to salinity. It allows you to slowly raise your salinity without shocking the inhabitants.

Steve1500 · Aug 15, 2019

Peace River said:
Yes, in line with what @Beonedge calculated, the sg of the added 20g is 1.035 which is above 1.024. Although this is mathematically correct, I would suggest that you top of with your regular mix of saltwater (or maybe 1.027 or even 1.028) instead of RO until it raised to the desired level of 1.026 to maintain stability in your tank.

Brain farted and reading to fast. I.035 is greater than 1.024! Thanks!

madweazl · Aug 15, 2019

While a calculator is probably handy, you can easily increase the salinity gradually over time when you perform the water change. Simply over fill a bit and let evaporation take over; as the water evaporates down to the desire water level, the salinity will increase.