Checking accuracy of Hydrometer in fresh water??

[fishy&co]

Hi,

My question is -
Can I test whether my hydrometer is in the ball park by seeing what it registers fresh water as?

Tank info (you don't have to read this) -
At the moment all that i have to measure salinity is a little glass hydrometer. Unfortunately it doesn't have any information regarding it's calibration.

Ok so i'll come clean and say i have not been the most attentive reef carer over the last year (no money :( ). But now i've started to get the tank ready for the introduction of corals. So i decided to dust off my hydrometer and test my water and it read 1.029! which i know is way too salty. However, my fish (blueface angel, flame angel and clown) have never seemed more healthy.

I live on the beach (20 metres from high tide) and collect fresh sea water for my tank. It the great sandy straights part of the aussie coast where the water is shallow, so i think that makes it more salty?? which is the cause of the problem. I top up with fresh rain water from a water tank (I think it might be high in phosphate - it's a concrete tank). Anyway my goal is to bring salinity down obviously by replacing tank water with fresh. I hope to buy a refractometer after christmas.



thanks

fishy&co

[gobind]

Hi 99% of us British hobbist don't use hydrometers any more. The most accurate way to measure salinty is buy using a refracometer

[fishy&co]

Hi gobind - i intend to buy a refractometer ASAP, but i am planning to do some largish water changes to try and bring the salinity down after the very high reading from my hydrometer (1.029).

[Randy Holmes-Farley]

The most accurate way to measure salinty is buy using a refracometer

I don't agree with that statement, but if properly calibrated with a seawater solution (which is not necessarily going to give the same result as calibration in pure fresh water) refractometers can be adequately accurate for reef aquarium use:

Refractometers and Salinity Measurement
http://reefkeeping.com/issues/2006-12/rhf/index.php

[Randy Holmes-Farley]

Can I test whether my hydrometer is in the ball park by seeing what it registers fresh water as?

What type of refractometer?

Unless it is a tall glass type, I'd test it with a DIY salt solution:

Reef Aquarium Salinity: Homemade Calibration Standards
http://reefkeeping.com/issues/2004-06/rhf/index.htm

[fishy&co]

Sorry yes it is the glass type - the one the you put in the tank.

[Randy Holmes-Farley]

If it reads low enough to read 1.0000, then checking RO/DI water is a good step and may be adequate. Checking the salt solution is a good second step to confirm that it was originally made correctly.