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Old 06-04-2012, 02:24 PM   #1
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Specific gravity

Is there any reason why my specific gravity would be slowly decreasing instead of increasing besides that my refractometer is not giving accurate readings? About 4 days ago it was 1.025, and over the last few days has slowly been going down to 1.023. I thought it was supposed to rise over time and I would top off with fresh water. Are there any tips to using a refractometer that maybe I'm not aware of? I used distilled water to calibrate, and have recalibrated a few times. I clean it off after every use. What else?
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Old 06-04-2012, 04:00 PM   #2
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Sounds like a refractometer issue. I'd purchase some calibrating fluid and check. Using rodi water to calibrate never worked for me. For now maybe get your water tested at an lfs?
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Old 06-07-2012, 10:42 PM   #3
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Ok thanks Aquarick. I ended up buying a new refractometer online (when I called the lfs, I asked if they had any and they said refractometer? Like to measure light with? And so I explained what it is, and they said, Oh no, we have hydrometers. Wow). I just got the new one tonight, I also got some calibrating fluid. The water is testing at 1.024 right now, so that's a relief. It hasn't been way off at least!
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Old 06-07-2012, 11:01 PM   #4
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Skimming and salt creep can lower salinity over some time. Just because you calibrated with distilled does not mean you should be getting fluctuating readings. The reading might be wrong but it should cause it to fluctuate. Something to be aware of.
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Old 06-08-2012, 02:29 AM   #5
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Originally Posted by apinkmanatee View Post
Ok thanks Aquarick. I ended up buying a new refractometer online (when I called the lfs, I asked if they had any and they said refractometer? Like to measure light with? And so I explained what it is, and they said, Oh no, we have hydrometers. Wow). I just got the new one tonight, I also got some calibrating fluid. The water is testing at 1.024 right now, so that's a relief. It hasn't been way off at least!
Ouch! Any LFS worth their salt would at least know what a refractometer is. Glad your salinity wasn't too far off. Let us know how your salinity changes over time.
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Old 06-10-2012, 07:39 PM   #6
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Skimming and salt creep can lower salinity over some time. Just because you calibrated with distilled does not mean you should be getting fluctuating readings. The reading might be wrong but it should cause it to fluctuate. Something to be aware of.

I do have a lot of salt creep...that makes sense. Thanks!
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Old 06-10-2012, 07:40 PM   #7
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Ouch! Any LFS worth their salt would at least know what a refractometer is. Glad your salinity wasn't too far off. Let us know how your salinity changes over time.
I know! I thought they were a good place but I definitely am going to take all of their advice with a grain of salt from now on (no pun intended!) And I will let you know! Thanks.
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Old 06-17-2012, 09:09 PM   #8
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Ouch! Any LFS worth their salt would at least know what a refractometer is. Glad your salinity wasn't too far off. Let us know how your salinity changes over time.
So this has been my numbers over the last week...
Monday 1.022 (I know this is a little low)
Tues 1.023
Wed 1.024 (did a 15% water change this day with 1.024 water)
Thurs 1.024
Fri 1.024
Sat 1.024
Sun 1.024

What the heck? Water is clearly evaporating off the top. How could it possibly be the same for four days?? This is with my new fancy digital refractometer. I really want to get this figured out before I add more fish.
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Old 06-17-2012, 10:59 PM   #9
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Weird. Have you been cleaning your refractometer with rodi water between readings? Not exactly sure how your digital version works, but for my optical refractometer I clean with rodi water between readings.
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Old 06-18-2012, 12:55 PM   #10
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Weird. Have you been cleaning your refractometer with rodi water between readings? Not exactly sure how your digital version works, but for my optical refractometer I clean with rodi water between readings.
No I was just wiping it with cloth. And DUH...I was using the same dropper for the calibrating and saltwater. I bet that contaminated both samples. So I cleaned the area with rodi water and used spoons to put the samples on (I only have one dropper...where do you even buy those??) It came up 1.025. That was last night, I also did it this morning and it was 1.025. Maybe this has been the problem. Rookie mistake. I will continue like this and see if it makes more sense now. THANKS for your help as always
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