Salinity and Temperature

[nleong]

Hi,

I have read somewhere that temperature plays a part in the measurement of salinity. So do i need to take that into consideration when setting a stable salinity for my 2footer ?

Its currently at 1.02 with temperature around 80F (due to the cold weather) Read somewhere that need to add about 0.002 or something at that temperature ?

[Tanzy]

Salinity of the seawater remains the same regardless of temperature. The salt in the tank can't suddenly walk out of the water. It's the specific gravity of the water that changes with the temperature.

SG is the density of the liquid compared to the density of pure water. So if the tank water SG is 1.025, it will be 1.025 times heavier than pure water. We measure SG because the devices used are cheaper than for measuring salinity. SG can be converted to salinity but most people just leave it as SG reading for convenience. The range is 1.022 - 1.027 at 27 degC. When you are measuring SG take note of the temperature of the water and you can compare it to a conversion table for the salinity but I feel that for a reef tank kept at the normal temperature range, the salinity shouldn't be that far from normal seawater if the SG falls within the range mentioned above. The more important factor will be to maintain a constant SG than the 'correct' SG.

1.02 is too inaccurate. How are you measuring it? You'll need 3 decimel points.

[nleong]

erm... sori to confused SG and salinity.

I'm using those floating type hygrometer (which have up to 0.002 calibration mark). Last night when the temperature was at about 80F, the SG was at about 1.022. But then this morning, i saw the temperature at about 77F, the SG dropped back to 1.02.

Erm... so at what SG should maintain it at ? Any plus or minus to take into consideration with relative to temperature ?

[Tanzy]

Are you sure? SG increases when temperature decrease assuming the salinity remains the same.

The SG to maintain is about 1.025 at 27 degC for Salinity of 35.

How big is your tank and were you dripping top up water overnight?

[nleong]

erm... yeah quite sure, unless i see parallex error. I will double check again tonight.

My tank is only 2ft, its still at the cycling stage. Thats y the temperature fluctuate quite significantly.

PH is dropping from 9 to 8.5, water yellowing. Just added a few LR last night.

All i have is an air stone pumping air rigourously. Off my canister a few days ago becos the pipe suddenly poped out from the outlet and flood the house and trip the mains ....

[Tanzy]

If your readings are correct, then the only way SG can drop is due to water being added. You mentioned airpump, so could it be that air bubbles are sticking onto the hydrometer and giving you inaccurate results.

[bawater]

Congrats nleong,

izzit your first saltwater & electricity experience. Hopefully no more.

i hate that 'POP' then the lights go out feeling. Watch out if u trip the switch box in the flat to often, if its too often it will trip the main box located outside your house(should be a dark blue/grey box around the front door-there's a small lock on it u gotta break). Keep that in mind if u can't seem to switch everything back on in the hse switch box.Oh! but firstmake sure u don't hear water dripping or make a mental note to go round the tank with a torchlight first otherwise power won't come back on.

The floating hydrometer is not the most accurate- u get a rough gauge from it(somethin like ok u got to keep salinity within 1.022 to 1.024)while its bobbing around in the tank.

i have one & also 2 needle types and comparing readings the floating one is slightly off, sometimes up to 0.01-0.02 difference. i gather that since the contents are metal beads held in place by wax of some sort+ the fact that the whole thing made of glass & it floats in the tank the whole day under light- may contribute to the difference in temp to salinity thing & somethin to consider.

another thing bugs me is the damn thing keep bobbing up & down-spinning round & round.

All are calibrated at water temp 25c,it says on the box when u buy it.

[nleong]

the SG is staying fix at 1.02 now. I know the floating type is not accurate, so i just want to make it to 1.022 for a rough guide. The hygrometer doesn't go up and down once it settle down. think i better go get those needle one and make a more accurate reading.

as for the tripping of main, well, i have done that before, even tripped the main switch outside, have to call town council and ask where to switch it back on. now i know where the switch is hee....

the only problem i have, is the nagging by mum. if the thing pop again, i think i will have to sell the canister....

[Tanzy]

Actually, those floating hydrometers are more accurate than those swing arm type. The proper way to measure SG is to pour the water into a measuring cylinder with a mercury thermometer then let the hydrometer stabilise. You are not suppose to leave it in the tank all the time, if stuff starts to grow on or coat the hydrometer glass it will become inaccurate.

Of course the best way is to get an electronic meter or a refractometer.

BTW, your SG is a bit too low, try to bump it up to 1.024 and when you say 1.02 I think you mean 1.020, please include the last zero to let us know the precision of your reading.

[sduu]

Hi Tanzy, Just read through the book "Corals" by Eric H.Borneman. He mentioned that "Recent trends favor maintaining somewhat more natural reef temperature of 27-29?C(90-84?F) and salinity of 35ppt is 1.027 sg of natural seawater. This are the targets to keep. Can we follow the experts advices??

[Tanzy]

My tank runs at about 27.0 +/-0.5 degC and salinity of 35.

SG depends on temperature. The temperature will have to be 20degC for the SG to be 1.027 at 35 salinity. A range of 1.024-1.025 will be more realistic.

[sduu]

Thanks Tanzy, btw my tanks temp is at 26?C and SG is at 1.023 abit low. should i add more salt mix to increase to 1.025. many many thanks

[Achilles Tang]

I keep my tank temp at 25 degrees and my sg at 1.025.

[Tanzy]

Thanks Tanzy, btw my tanks temp is at 26?C and SG is at 1.023 abit low. should i add more salt mix to increase to 1.025. many many thanks

If the guys living in the tank think it's fine then just leave it. If you want to increase it then do it slowly.