Specific Gravity/Hydrometer question

[Twout]

Sorry about the question, but maybe this'll be helpful/interesting to others as well.

From the forums, I get the general consensus that specific gravity should optimally be 1.024 to 1.026. However, I have two hydrometers and one has a target range of 1.020 to 1.025 and the other indicates 1.020 to 1.023. I think this is the case with most hydrometers.

Why do they indicate a lower range than what the consensus range seems to be. If I'm not mistaken, natural seawater is somewhere in the 1.024 to 1.026 range?

Thanks!

P.S. Anyone have recommendations for a good thermometer? One of my hydrometers is also a thermometer and I bought a digital one with a probe I stick into the water and they differ by 2 degrees, which is exceedingly frustrating.

[gwen_o_lyn]

You can add specific gravity to the long list of topics widely debated in this hobby. I used to aim for 1.022-1.023 until I met Rob. And now I like to keep my tanks at 1.025.

Check into getting a refractometer- they are very accurate and more user friendly.

[CarmieJo]

For FO a lower SpG is thought to lower the incidence of parasites and many people keep their tanks at around 1.020. However for a reef you want to maintain your tank at a level closer to NSW which is 1.025.

[Twout]

Gotcha, that seems to make sense. I think I'll aim for NSW even though my tank's only a FOWLR since it is, well, natural. Thanks!

[CarmieJo]

If you already have fish in your tank change the SpG slowly.

BTW, as far as a thermometer goes I use a temperature controller so I can't make a recommendation. There is a little stick on thermometer on my sump but it is about 3 degrees lower than my temperature controller.

[Rob]

yep, Carmie nailed it..
"generally" in a FO tank lower SG eases respiration on the fish, my clown babies are kept as low as 1.015, and some go as low as 1.011. this is done to reduce the stress and work that the fish must do to stay alive and hydrated. ultimately i get them up to 1.025 but you get the point..
and as carmie noted as well, it has been shown (anecdotally, as i have read a paper on it) that lower SG can help prevent or rid fish from certain parasites or other unwanted diseases

i personally keep my reef at 1.025-1.026

[PreauxPhoto]

I’m a 1.024-1.025 type of guy but as gwen said it’s debatable. As far a thermometer’s are concerned when I take mine out to clean it I will stick it in a glass of ice water that has sat for at least 5 minutes and stirred before I put it in it should read 32° then I will place it in my armpit and wait of it to read 97°. If it reads well I’m good to go if it reads let’s say 34° and 99° I know to adjust by 2°. Hope this helps!