Salinity drop question...

Ready4Launch · Mar 19, 2019

My salinity has normally been pretty good or a tad on the higher side historically. But, now, in less than a week, my salinity has dropped more than I'm used to seeing change.

I just calibrated my refractometer during my last reading too.

Today...
Salinity: 1.021
pH: 8.0
Ammonia: 0
Nitrite: 0
Nitrate: 7.5
Phosphate: 0
KH: 7
Ca: 420
Mg: 1275

3 days ago...
Salinity: 1.024
pH: 8.0
Ammonia: 0
Nitrite: 0
Nitrate: 10
Phosphate: 0
KH: 8
Ca: 435
Mg: 1305

I'm not used to seeing my salinity fluctuate more than 0.001 between readings. I realize it's not VERY drastic, but I'm curious if it is "normal" or if there is something else.

JasonK84 · Mar 19, 2019

Was a water change performed between the time of those readings?

Captain Quint · Mar 19, 2019

Have you by chance done a RODI freshwater top off a bit more than needed?

Ready4Launch · Mar 19, 2019

JasonK84 said:
Was a water change performed between the time of those readings?

No - have been trying to cut back the water changes to see the effects actually!

Ready4Launch · Mar 19, 2019

Captain Quint said:
Have you by chance done a RODI freshwater top off a bit more than needed?

I have an ATO hooked up.

Eagle_Steve · Mar 19, 2019

Ready4Launch said:
No - have been trying to cut back the water changes to see the effects actually!

How about skimmer activity? Have you had to dump the skimmer more? Tank size would also help as well. As a smaller tank will notice a fluctuation more than a larger one. Salt creep could also be a factor with evaporation and topping of with rodi water with the creep not factored in.

Ready4Launch · Mar 19, 2019

Eagle_Steve said:
How about skimmer activity? Have you had to dump the skimmer more? Tank size would also help as well. As a smaller tank will notice a fluctuation more than a larger one. Salt creep could also be a factor with evaporation and topping of with rodi water with the creep not factored in.

I've been more regular during the week to dump out the skimmer cup, but the adjustment has stayed the same.

Tank is a 120.

Sod Buster · Mar 19, 2019

Calibrate everytime for a "check". Test the new mixed water before it goes in the tank everytime. I nuked a pretty nice tank using a fancy 3 part mix salt. Started looking crappy, so multiple water changes later, dummy me didn't realize component B had precipitated in the jug until the Crystals poured out into the cup. Learned the hard way cause I fell into a hurried routine.

Ready4Launch · Mar 19, 2019

Sod Buster said:
Calibrate everytime for a "check". Test the new mixed water before it goes in the tank everytime. I nuked a pretty nice tank using a fancy 3 part mix salt. Started looking crappy, so multiple water changes later, dummy me didn't realize component B had precipitated in the jug until the Crystals poured out into the cup. Learned the hard way cause I fell into a hurried routine.

Yeah, but I changed water. Measurements after that, salinity was fine. No water adds or changes since other than ato.

Sod Buster · Mar 19, 2019

I would say wet skimming then.

Super Fly · Mar 19, 2019

lower salinity leads me to believe that either the ATO is adding too much water (diluting the salt level) or the refractometer is not reading correctly. I'd check the ATO float/sensor and water levels to ensure it's not higher than normal and test using another refractometer.

I calibrate refractometer weekly AND keep the equipent same/close to tank water temp. I have noticed different salinity readings when refractometer did not match tank water temp.