Salinity Dropping/Staying Low?!

guitarvp · Feb 15, 2016

I am stumped. My 100g with sump has been up for about a month now and just finished cycling. However, the salinity has consistently stayed at 1.020-1.021 (Red Sea Refractometer). I tried raising it to 1.025 when I did a water change this past weekend. Shortly after the PWC the refractometer read 1.025. Within 24 hours it was back down to 1.020. I've even let the water level in the return chamber in the sump drop down 3-4 inches and the salinity continues to read 1.021. I never had this issue with my previous nano and I feel like I am going crazy. Could it be something with the refractometer or is it user error. I just added the clean up crew yesterday and I want to get the salinity stable and somewhere between 1.023 and 1.025.

Any help or advice is greatly appreciated.

SteveSTL · Feb 15, 2016

Have you calibrated the refractometer? Is there a local store (or another hobbiest) with a refractometer who can double check it?

guitarvp · Feb 15, 2016

I have, I used RO/DI to get it to zero. I am going to an LFS today and will take some water with me to have them double check it. It's just weird that even with evaporation, the refractometer is reading the same thing.

TheEngineer · Feb 15, 2016

It takes a lot of salt to raise 100g up by 9ppt (difference from 1.020 to 1.025). That's 9g/liter that you need to add. Or in your case 3406 grams. That's 7.5lbs of salt.

guitarvp · Feb 15, 2016

icecool2 said:
It takes a lot of salt to raise 100g up by 9ppt (difference from 1.020 to 1.025). That's 9g/liter that you need to add. Or in your case 3406 grams. That's 7.5lbs of salt.

Thanks for the reply. I am going to try raising it slowly over the next day or so.

TheEngineer · Feb 15, 2016

Make sure your reading is correct first. The only way for your salinity to drop that much is for that much salt to have come out of your tank. That means you would have lost 100 liters of saltwater. Is that possible?

EDIT: Whoops! I said 100gallons first. Should have been 100 liters. That's 26.5 gallons.

McMullen · Feb 15, 2016

Definitely double check the salinity. Great reply from "icecool2" This has to be an error in measuring and or calibration. Even a loss of water volume from the tank should yield the same salinity level. Only through evaporation or adding RODI without salt mix would produce large changes like you've described.

fragit · Feb 15, 2016

Refractometers are not supposed to be calibrated with RO/DI water!! You should be calibrating it with a calibration fluid that is 35ppm. You can get it at bulk reef supply or probably your LFS.

guitarvp · Feb 15, 2016

Thanks for all the replies folks. Gonna wait to raise salinity until I have an accurate reading. There is now way I've lost the much water (26g) so it's either me or the refractometer.

fragit said:
Refractometers are not supposed to be calibrated with RO/DI water!! You should be calibrating it with a calibration fluid that is 35ppm. You can get it at bulk reef supply or probably your LFS.

Fragit- I just ordered calibration fluid through Amazon. Should be here later today. Although, I've used RO/DI in the past and I've never had a problem. Either way, I'm going to use the calibration fluid to make sure it's 100%.

Randy Holmes-Farley · Feb 15, 2016

guitarvp said:
I am stumped. My 100g with sump has been up for about a month now and just finished cycling. However, the salinity has consistently stayed at 1.020-1.021 (Red Sea Refractometer). I tried raising it to 1.025 when I did a water change this past weekend. Shortly after the PWC the refractometer read 1.025. Within 24 hours it was back down to 1.020. I've even let the water level in the return chamber in the sump drop down 3-4 inches and the salinity continues to read 1.021. I never had this issue with my previous nano and I feel like I am going crazy. Could it be something with the refractometer or is it user error. I just added the clean up crew yesterday and I want to get the salinity stable and somewhere between 1.023 and 1.025.

Any help or advice is greatly appreciated.

What did you do to raise the salinity that much by water change? You'd need a big change with very high salinity water.

I'm wondering if temperature is impacting your readings. Does the tank temp vary a lot? does the room temp where you take the measurement vary?

Is the refractometer an ATC (automatic temperature compensation) type?

guitarvp · Feb 15, 2016

Randy Holmes-Farley said:
What did you do to raise the salinity that much by water change? You'd need a big change with very high salinity water.

I'm wondering if temperature is impacting your readings. Does the tank temp vary a lot? does the room temp where you take the measurement vary?

Is the refractometer an ATC (automatic temperature compensation) type?

I did a PWC with 35g at 1.030, maybe not high enough to offer any substantial increase. The temp in the tank runs between 78-79 degrees as I have it on an Apex. The room temp is pretty constant at about 77 degrees.

Yes the refractometer is the Red Sea with the ATC.

Randy Holmes-Farley · Feb 15, 2016

35 gallons of 1.030 changed into 100 gallons of 1.020 would bring the sg to 1.0235. Not sure why you saw a higher value initially unless it wasn't mixed in, or why you saw a lower value later, but it must be a testing issue of some sort.