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Old 11-06-2008, 08:33 PM   #1
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Unhappy Specific gravity vs temprature

I was just wondering, if I am doing a water change and I mix my salt with cold RO water (60 deg F) and bag salt how do I tell what the specific gravity of my water is relative to the water in my tank at 75 deg F. (1.022 grav) I followed the mix instructions and my salinity seems to be 1.030 with the water/salt mix, a bit salty I belive? furthermore am I shocking my fish/ coral by doing a change that cold at 10 percent the total volume?
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Old 11-06-2008, 08:35 PM   #2
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yes, the water should be same temp as the tank and same salinity.
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Old 11-06-2008, 08:42 PM   #3
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What are you using to measure your SG? if you have a swing arm hydrometer those can be inaccurate and most likely the source of your problems long before the change in temperature. You should let your mixed saltwater sit for 24 hours before adding it to the tank and try to keep it at least close to your tank temp. If its cold just try to add it slowly into the streams of a power head so it gets mixed in and you don't have any big changes in your water temp.
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Old 11-06-2008, 08:52 PM   #4
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Get a ATC (auto temp compensating) Reefractometer. They are far more accurate then the swing arm hydrometer.
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Old 11-06-2008, 08:59 PM   #5
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im using a hygrometer the floating kind, I heard that they are mostly calibrated at 60 deg F and beings this is something I bought as a package second hand I don't have any documentation. I'm just limping through until I can spring for a reefractometer I'm just kinda worried I have to do a partial asap because the ammonia reading I took today was what looked to be between 0 and 0.25 although my nitrates are at ~0.3 so maybe I just overlaoded the bacteria and need to wait it out (seems to be a lot of deterius, chock one up to over feeding) otherwise I am totally good to wait 24 hours to match temp and gravity.. what do you guys think ?? (I also have some amquel that claims to remove ammonia but i don't think I want to go that far yet, natural is best over dosing, at least from what Ive read so far)
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Old 11-06-2008, 09:07 PM   #6
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Check on marinedepot.com for your refractometer. I picked one up for $35. If you have a spare powerhead drop that in the bucket or container you mix your SW in to keep things moving and the heat the pump generates will help warm the water.
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Old 11-07-2008, 12:12 PM   #7
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I agree definately get a refractometer money well spent. And Temperature affects the reading even with the ATC Refractometers IMO. My RO/DI unit is connected behind my washing machine and the line runs threw a hole I drilled into the wall to my 32gallon trash can where I store RO/DI water with a heater. Than I have a 20gallon trash can I use to mix saltwater. I take water from the 32G to the 20G with a Pitcher. I fill the 20g close to the top. And then I add exactly 19 scoops of Reef Crystals. I comes out perfect everytime. After 24 hours of sitting with a powerhead and heater its ready to go. I usually refill both cans after I do the PWC so the water actually sits for about a week.
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Old 11-07-2008, 06:53 PM   #8
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The hydrometer will give you false readings at lower temps. I did the same thing when I first started. I kept adding salt and more salt but the readings went up only a little....Definitely get the refractometer, it should adjust to the temp of your water.
One more thing, it is best to add a ph and heater to premix your water for at least 24 hours.
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Old 11-07-2008, 07:03 PM   #9
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I totally agree with the 24-48 hr wait. Then test your SW
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