The Great Specific Gravity Debate

[Feron]

So I've been noticing in alot of posts the differing oppinions on the salinity of water in the various types of marine tanks.
I've always thought that seawater was on average 1.023 and that as long as the range was close, with no great changes in salinity, that stock would survive well.

I'm curious as to:
1) What people's specific gravities are at on avg
and
2) Why?

Thanks for inputs!

[JM]

I feel that 1.023 is a safe SG for a tank with any species of fish. Different fish come from different bodies of water where the SG is slightly different, but they will all acclimate with time. I have heard that keeping your tank at a lower SG will help prevent illness because certain bacteria and other micro organisms cannot acclimate to the lower SG which causes them to die. I have a shark and i keep his tank at a slightly higher SG because i have read books about aquarium sharks that say they do better at slightly higher SG.

[melosu58]

1.023 - 1.024
Why? Because it has worked for 8 years

[Phyl]

I generally run my SPS tank between 1.025 and 1.028 (trying to stay on the 1.025) but don't see any ill effects when it runs on the high side. I do use a refractometer and would say that if you're using a hydrometer you should steer closer to the 1.022/3 than 1.025 as they tend to err on the side of being high.

My softie tank I run closer to 1.024/5 but I get seriously less evap on that tank than my prop system.

[Fluff]

Mine stays around 1.025-1.026

[Brenden]

I keep mine at 1.025. Natural SW "normally" is between 1.025-1.027

[cmor1701d]

I also keep mine at 1.025-1.026.

[fishfreek]

I shoot for 1.025 but IMHO its not what the SG level is its how stable the level is. I honestly dont care if you keep your tank at 1.020 or any level between 1.020 - 1.030 as long as its stable.

Stability is the name of the game in reef tanks. For fish only tanks a lower salinity has been said to ward off parasites where as a reef tank usually shoots for a higher salinity due to the corals. If your tank is stable at 1.024 and does not swing much than thats just as good im by book as a tank with a SG of 1.025. .001 change in salinity is NOT going to make a tank crash or be a great sucess. If this was the case then what about the coral reefs that are close to the shore when there is a big rain storm and there are significant amounts of 1.000 water flowing into the ocean. There will be areas and periods where the SG changes. Often times during high tide corals are left high and dry above water or they are left in tidal pools where the water evaporates over the period of low tide causing the salnity in those small tide pools to increase only to have the salinity change once high tide comes back in.

If .001 salinity was that big of a deal than you would not find corals in tidal pools nor would you find them where large bodies of freshwater dump into the sea to cause periods of lower salinity.

[Feron]

Good points fishfreek..
To dig a little deeper on those points (curiousity!), why arn't we aiming for a fluctuation like that (gradually of course) to and fro? Not talking a major shift, but does a 'pattern' (other then a constant) better reflect nature, and therefore better - or does nature just 'ignore' the sublties?
Prolly just too much trouble and too easy to go awry to bother with.. just conjecture..

[fishfreek]

Those fluxuations would not bee seen over the entire reef nor would they really be reflected in the deeper reefs. I was being more general to the very shallow reefs and how if corals in general where that sensitive to an exact salinity there would be no corals in the shallows.

Why do we not try ti emulate nature more. Probably cause its to darn complex. Only the most complex systems have lighting on tracks to simulate the suns movements during the day. Only the most complex of lighting setups simulate breif periods of cloud cover or X% of days per month with total cloud cover. Those of us with moon lights dont simulate the phases of the moon either for the most part.

[Feron]

Funny you mention the lightning thing.. I had actually tried to work out doing something like that for a friend with a 1200g tank lol
(We have a machine shop at our disposal and were thinking of a belt driven system with MHs that moved every quarter hr (extra distance beyond tank for dusk/dawn) as well as led's for the moon light on a similar setup.)
He has a controller so we could easily dim/shut off the light for phases and the odd occasional solar eclipse.

Our biggest problems were 1) heat 2) not catching his house on fire and 3) recessing the deal (more heat, more potentially burning of the house)

Fun to dream up tho

(and hey, I have ocean sounds playing very softly near my tank..if only to soothe the rock atm)

[Jeraljay]

in the pool industry we measured pool salinity in PPM, the avereage salt water pool should be around 3200 ppm, the ocean I heard was wround 30000 ppm. What unit of measurement do you guys use in determing SG?

[Brenden]

SW tanks are also measures in ppt. The ocean is around 35ppt which is roughly equal to 1.027

[drillsar]

Mine 1.025-1.026 closer to the 1.026 side.

[Choas]

Mine is at 1.025.