Specific Gravity

[mjvincent]

I just completed a water change this past Friday... Today I was testing the water and noticed my SG was 1.026-1.027 (depending on which reading I was doing with the deep six). I had initially had the tank at 1.025 and I was wondering if I should leave things be or drain about a gallon out and replace with fresh ro water (no salt). I know salinity varies greatly in different areas, but wanted to be sure that I wasn't causing any troubles for my damsels and my tree coral...

Thanks, Mike

 

[TCTFish]

SG does not vary greatly in the ocean. Where freshwater meets saltwater it does like estuaries and lagoons, but not the ocean. The SG is border line high. I've seen fish and coral break down in SG above 1.027. The best thing to do is exchange a small amount of water and replace with RO every few hours until the SG is down to about 1.024

 

[IfoundNemo]

SG recommendation is 1.023 - 1.024 so at 1.025 is still a litle high. JMO.

 

[steve-s]

SG recommendation is 1.023 - 1.024 so at 1.025 is still a litle high. JMO.

Why

Cheers
Steve

 

[ZoozFishMaster]

I think natural sea water has a specific gravity of 1.026 - 1.027. I always keep my tanks at 1.025 with no adverse effects. Actually, I think the invertebrates do better and protein skimmers work more efficiently in systems that maintain a specific gravity close to natural sea water. JMO.

 

[cmor1701d]

Are you rinsing with fresh water between readings?
Did you calibrate it against a known sample, e.g. a refractometer?

I found my deep six to vary from reading to reading so I spent the bucks to get a refractometer. Well worth it.

As an aside...
Different oceans have slightly different specific gravities. The tropical Indo-Pacific has an average specific gravity of 1.022 - 1.025. The Caribbean has an average specific gravity of 1.023 - 1.026. The Red Sea has an average specific gravity of 1.028 - 1.035. The specific gravity changes in each area are due largely to rain fall.

 

[mjvincent]

I figured out what I did... I forgot to account for the temperature change that I made after cycling my tank. I had the tank at approx 81 degrees help cycle the tank. After cycling the tank I dropped the temp to 79 degrees which raised the reading of my tank... Here is a table I found that you might find helpful...

Degrees F. Hydrometer reading.
50 1.0255
55 1.0252
60 1.0250
65 1.0246
70 1.0240
75 1.0233
80 1.0226
85 1.0218 (rather hot for most tanks)
90 1.0210 (very hot for most tanks)

Found at http://www.fishprofiles.net/faq/reef/reefkeeper1.asp#1.3.6