Salinity drop??

Thepopo · 03/13/2010, 09:51 PM

Hi guys! This place has been great to answer all my questions. But I have a problem that I can't figure out. I started my reef tank a few weeks ago. My salinity was around 1.021 at the time. I was getting the hang of it and decided to let it evaporate till it got to the salinity I wanted since I couldn't find a formula for raising salinity point by point after I added the water to the tank. Anyway the salinity kept rising till it got to 1.0245. that was a few days ago I last measured. I added a piece of limestone rock to the water yesterday. And now today my salinity is 1.021. I don't have a refractometer but I have two different hydrometers and they both gave me the same reading. Is it the limestone sucking up salt or did some cycling occur that took the salt with it? I thought salt wouldn't leave the tank. Its been a short time so I don't think salt creep is a issue. It's a 40 gallon tank with temperature at 75F.

Thx!

rayjay · 03/14/2010, 12:24 AM

It's possible that you just haven't learned the knack of using your hydrometers yet.
IME, I've found first of all, to keep them cleaned with white vinegar and rinse well between use after having their readings compared to a known and trusted s.g. source.
When using, if it's the swing arm type, very slowly dip it into the water to lessen the chance of micro bubbles forming on the swing arm. (they are small and hard to see)
Some types you can reach in with something thin and tap the float to release the bubbles.
In any case, I take a minimum of three readings, finding the first reading has a higher chance of error until the hydrometer has been "wetted" sufficiently. The second reading is more likely to be the correct one, and the third, just to verify.
I find mine can take quite a bit to finally settle at the proper reading so don't rush it.
If you are using a floating hydrometer, it will not be accurate by floating it in the tank. However, use a column cylinder to gently lower the hydrometer into the sample water until it just floats without bobbing. Water can adhere to the stem above the float mark, causing slight error in the reading.
You may have had erroneous readings either at the start, or at later times to produce the seemingly impossible result.
Most people nowadays are using refractometers, but I've found that many refractometers are not giving proper readings either because it was the wrong refractometer for the application, or that they were improperly calibrated, many times using water to calibrate.

Randy Holmes-Farley · 03/14/2010, 07:59 AM

To Reef Central

I suspect you are seeing testing error/inaccuracy. Salinity won't drop on its own like that, unless you remove salt water and replace it with fresh water.

How are you measuring salinity?

Thepopo · 03/14/2010, 07:57 PM

I washed the swing arm hydrometer with vinegar to remove any deposits it could have built up. I did notice a tendency for the swing arm to build up bubbles. I am using both a swing arm type and the floating type. I thought it could be the rock since I had my Crocea on it and the sucker jumped clear off it by the next day. It's a piece of limestone rock I picked up in the farm.

Thepopo · 03/14/2010, 08:02 PM

Thx for the welcome

. I look forward to learning a lot from you guys.

Amp2020 · 03/14/2010, 09:13 PM

Water temperature will affect the readings

Thepopo · 03/14/2010, 09:32 PM

Ya I know. I been keeping a close eye at the temperature gauge. I even tested at ambient temperature as well. I am adding salt now to raise it up little by little. I am gonna do a experiment with the type of rock i used and see if the water I put it in changes or if it was all air bubbles or salt build up in the meter that was giving me those readings. It's probably the meter though.

Randy Holmes-Farley · 03/15/2010, 06:53 AM

FWIW, swing arm hydrometers are notoriously inaccurate and/or variable, so I would not assume your tank has been experiencing any unusual salinity changes.

03/13/2010, 09:51 PM	#1
Thepopo Registered Member Join Date: Mar 2010 Posts: 140	Salinity drop?? Hi guys! This place has been great to answer all my questions. But I have a problem that I can't figure out. I started my reef tank a few weeks ago. My salinity was around 1.021 at the time. I was getting the hang of it and decided to let it evaporate till it got to the salinity I wanted since I couldn't find a formula for raising salinity point by point after I added the water to the tank. Anyway the salinity kept rising till it got to 1.0245. that was a few days ago I last measured. I added a piece of limestone rock to the water yesterday. And now today my salinity is 1.021. I don't have a refractometer but I have two different hydrometers and they both gave me the same reading. Is it the limestone sucking up salt or did some cycling occur that took the salt with it? I thought salt wouldn't leave the tank. Its been a short time so I don't think salt creep is a issue. It's a 40 gallon tank with temperature at 75F. Thx!

03/14/2010, 12:24 AM	#2
rayjay Premium Member Join Date: Oct 1999 Location: London, Ontario, Canada Posts: 2,981	It's possible that you just haven't learned the knack of using your hydrometers yet. IME, I've found first of all, to keep them cleaned with white vinegar and rinse well between use after having their readings compared to a known and trusted s.g. source. When using, if it's the swing arm type, very slowly dip it into the water to lessen the chance of micro bubbles forming on the swing arm. (they are small and hard to see) Some types you can reach in with something thin and tap the float to release the bubbles. In any case, I take a minimum of three readings, finding the first reading has a higher chance of error until the hydrometer has been "wetted" sufficiently. The second reading is more likely to be the correct one, and the third, just to verify. I find mine can take quite a bit to finally settle at the proper reading so don't rush it. If you are using a floating hydrometer, it will not be accurate by floating it in the tank. However, use a column cylinder to gently lower the hydrometer into the sample water until it just floats without bobbing. Water can adhere to the stem above the float mark, causing slight error in the reading. You may have had erroneous readings either at the start, or at later times to produce the seemingly impossible result. Most people nowadays are using refractometers, but I've found that many refractometers are not giving proper readings either because it was the wrong refractometer for the application, or that they were improperly calibrated, many times using water to calibrate. __________________ 490g soft lps clams tangs b'flies clean wrasses, seahorses. All tanks lit with N.O.fluor., most Berlin method. No clean up crews. See website for N.O. fluor. pics. Culture nanno, rotifers and brine shrimp. Current Tank Info: Seahorses, Reef, and Fish only

03/14/2010, 07:59 AM	#3
Randy Holmes-Farley Reef Chemist Join Date: Apr 2001 Location: Arlington, Massachusetts Posts: 81,937	*To Reef Central* I suspect you are seeing testing error/inaccuracy. Salinity won't drop on its own like that, unless you remove salt water and replace it with fresh water. How are you measuring salinity? __________________ Randy Holmes-Farley Club 65535 Current Tank Info: 120 mixed reef

03/14/2010, 09:13 PM	#6
Amp2020 Registered Member Join Date: Oct 2007 Location: Richmond near A.A. Posts: 1,202	Water temperature will affect the readings __________________ Victor Current Tank Info: None.

03/15/2010, 06:53 AM	#8
Randy Holmes-Farley Reef Chemist Join Date: Apr 2001 Location: Arlington, Massachusetts Posts: 81,937	FWIW, swing arm hydrometers are notoriously inaccurate and/or variable, so I would not assume your tank has been experiencing any unusual salinity changes. __________________ Randy Holmes-Farley Club 65535 Current Tank Info: 120 mixed reef

03/14/2010, 07:57 PM	#4
Thepopo Registered Member Join Date: Mar 2010 Posts: 140	I washed the swing arm hydrometer with vinegar to remove any deposits it could have built up. I did notice a tendency for the swing arm to build up bubbles. I am using both a swing arm type and the floating type. I thought it could be the rock since I had my Crocea on it and the sucker jumped clear off it by the next day. It's a piece of limestone rock I picked up in the farm.

03/14/2010, 08:02 PM	#5
Thepopo Registered Member Join Date: Mar 2010 Posts: 140	Thx for the welcome . I look forward to learning a lot from you guys.

03/14/2010, 09:32 PM	#7
Thepopo Registered Member Join Date: Mar 2010 Posts: 140	Ya I know. I been keeping a close eye at the temperature gauge. I even tested at ambient temperature as well. I am adding salt now to raise it up little by little. I am gonna do a experiment with the type of rock i used and see if the water I put it in changes or if it was all air bubbles or salt build up in the meter that was giving me those readings. It's probably the meter though.