Odd drop in salinity and calcium

[Steve Fast]

Hoping someone here might have some ideas... First a bit of background. The tank is 550 gallons with two 150 gallon sumps. Today when testing I noticed that the refractivity dropped from 34 last week to 24 this week. Also, calcium dropped from 450 last week to 350 this week. I took both of these measurements twice with different instruments. Alkalinity has held steady at 9.3 and pH steady at 8.3. The sump nor the tank have higher water levels than before. The skimmer has only pulled about 1 gallon over the last week. There were no water changes either. I have not found anything similar in anywhere on the web. Coral and fish all are OK. I’m completely baffled about what might have happened. Any ideas?

 

[gbroadbridge]

Hoping someone here might have some ideas... First a bit of background. The tank is 550 gallons with two 150 gallon sumps. Today when testing I noticed that the refractivity dropped from 34 last week to 24 this week. Also, calcium dropped from 450 last week to 350 this week. I took both of these measurements twice with different instruments. Alkalinity has held steady at 9.3 and pH steady at 8.3. The sump nor the tank have higher water levels than before. The skimmer has only pulled about 1 gallon over the last week. There were no water changes either. I have not found anything similar in anywhere on the web. Coral and fish all are OK. I’m completely baffled about what might have happened. Any ideas?

The measurements are wrong.

 

[WalkerLoves_TheOcean]

No idea why, just please make sure to raise that salinity up very slowly.

 

[Steve Fast]

just to clarify. I used two different Milwaukee digital refractometers and then one of those you look through. Used Salifert and Hanna for calcium. The values have held steady for over a year until now.

 

[Steve Fast]

No idea why, just please make sure to raise that salinity up very slowly.

thanks. was thinking about doing that though wanted to check first. it's a lot of salt plus i do not know mow much the alkalinity and magnesium will be effected

 

[gbroadbridge]

Hoping someone here might have some ideas... First a bit of background. The tank is 550 gallons with two 150 gallon sumps. Today when testing I noticed that the refractivity dropped from 34 last week to 24 this week. Also, calcium dropped from 450 last week to 350 this week. I took both of these measurements twice with different instruments. Alkalinity has held steady at 9.3 and pH steady at 8.3. The sump nor the tank have higher water levels than before. The skimmer has only pulled about 1 gallon over the last week. There were no water changes either. I have not found anything similar in anywhere on the web. Coral and fish all are OK. I’m completely baffled about what might have happened. Any ideas?

Like I said above the measurements are wrong.

It is not possible for the salinity to drop without affecting Alkalinity unless you have changed dosing.
If you have not lost water it is not possible for salinity to drop. It has to go somewhere.
Do you have a leaking pipe?

 

[piranhaman00]

Yup measurements are wrong. What you are describing is not possible. Check calibrations, ect.

 

[dschuffert]

I agree with several others who have responded. I think the measurements are inaccurate. I suggest you calibrate your instruments and take another measure. I like using reference solutions that are certified at a certain number and then compare to the results of the instruments I am using.

 

[Tripod1404]

Could the past measurement at 34 ppt be wrong (i.e. it was always at 24)? A drop from 34 to 24 ppt on a 850 gallon system would require something like 250 gallons of saltwater to be replaced with RO/DI water. One of the measurements is certainly wrong.

 

[Randy Holmes-Farley]

It could be either or both measurements are wrong, but here's why it is obvious the measurements are wrong.

If you start with 900 gallons of water at 34 ppt, and want to get to 24 ppt, you would need to replace 375 gallons of the salt water with fresh water. Unless that might have happened without your knowing, the measurement is in error.