Salinity Won’t Stay The Same

[franktobia]

I’ve have been trying to lower my salinity for a little over 2 months. For the first year of my tank, I used pre mixed salt water from my LFS. The salinity was way to high so I bought an Rodi machine to try and fix the salinity levels. I have only been putting RODI water in the tank which temporary helps the levels down to a normal level right after my water change. But after a week, the levels go up back to way over the top. How is this possible since i’m not using salt water? Could it be my bucket since I use it to remove water from the tank too?

 

[Sniperhank]

Evaporation. Water evaporates and the salt is left behind.
It takes daily addition of water to replace what evaporated to keep salinity stable. This is why many employ automatic top offs to their systems to keep from rising.

 

[franktobia]

Evaporation. Water evaporates and the salt is left behind.
It takes daily addition of water to replace what evaporated to keep salinity stable. This is why many employ automatic top offs to their systems to keep from rising.

How much water would I need to add each day to avoid a change in my salinity for a 37 gallon tank.

 

[Sniperhank]

That varies from system to system and time of year.
I had a 55 that would have a gallon of water evaporate every day.
Now I’m running a 125 that does under that in a day during non winter months.

 

[coralbandit]

What is your salinity reading and how are you reading it [what are you using? ]hydrometer, refractometer or digital...
I'll guess a hydrometer...
Salt can not increase with out addition. Some increase is noted if you let enough evap happen without topping off ,but in a 37 you would need to let more then you should evap for it to be a serious issue IMO.

 

[franktobia]

What is your salinity reading and how are you reading it [what are you using? ]hydrometer, refractometer or digital...

I'll guess a hydrometer...

Salt can not increase with out addition. Some increase is noted if you let enough evap happen without topping off ,but in a 37 you would need to let more then you should evap for it to be a serious issue IMO.

Using a refractometer. Right now before a water change my salinity is 1.031. Last week after my water change, it was around 1.028. I’ve never topped off my system in the year and 1/4 that it’s been running. Since I do weekly water changes, I would just add enough so it would get up to the right spot so my protein skimmer could run properly.

 

[coralbandit]

Then it does sound like evap is what is causing your high levels . How low does the water go from water change to water change ? Do you remove water during your water changes? How much do you take out and add back? You only add back Ro no salt ?

 

[franktobia]

Then it does sound like evap is what is causing your high levels . How low does the water go from water change to water change ? Do you remove water during your water changes? How much do you take out and add back? You only add back Ro no salt ?

Every weekend I do a water change. So every week so time between Fri Night-Sunday it’s getting done. I take out 4-5 gallons and then add around 6 gallons of RODI water with no salt.

 

[Sniperhank]

Just sounds like the salinity is building up because it is being replaced by salt water rather than ro/di. It is probably barely noticeable due to very low evaporation. Sounds like a dream...

 

[PhylumCnidaria]

You can have partial freshwater in your water change, or just remove leftover water