View Full Version : Idea for future meeting project.........

03/22/2004, 06:35 PM
At the last meeting I borrowed a swing arm hydrometer from Brian because my floating glass hydrometer had broken. (refractometer's on backorder) Since James had a refractometer and swing arm hydrometer we did some testing and discovered one hydrometer was off by 3/100ths.

It came up to have everyone attending a meeting bring whatever they use to test SG and test it in comparison to a known sample and calibrated refractometer backup. Some hyrometers can't be adjusted, but you can adjust the markings to reflect actual readings.



03/23/2004, 06:39 PM
I have two of the exact same hydrometers, Aquarium systems swing arm types. Neither of them read the same. one is off by almost 5/100ths.

04/02/2004, 06:26 AM
Do you both mean thousandths? Or ten-thousandths? Or were they off that much? I am not sure what the refrac-to-meters read, being they read salinity and the hydrometer reads SG. Do they read all metal salts or just sodium chloride? Checking with Motes lab here and down in the Keys the salinity of the gulf here and gulf and atlantic down in the Keys is between high 34s to low 36s in salinity. Averages high 35s. Our water out here is usually 1.0255 SG according to my meters. Sometimes it will be 1.027, here and in the Keys. Adding salts of calcium , sodium bicarb and sodium carbonate, magnesium chloride, strongium,(all salts) etc will raise the SG accordingly. What I do is check often, but I use water from the sea and I check it to my water. I have 2 of the swing arm SG meters. Stability is the thing you want to achieve. I do know from working shipwrecks in the Caribbean and using underwater metal detectors there for many years, that the water in the Virgin Islands is very salty and is so salty that it will make the underwater detector false, indicating metal (in salt) so that we have to lower the sensitivity more than other places. It gets higher here during late spring/early summer when we have droughts. Go to search on the web for NDBC-Florida which is National Data Bouy Center run by NOAA and it will tell the salinity of water all over the gulf and east coast etc. Plus air and water temp, wave height, history etc. I use it to check waves and wind plus this time of year for water temp, because I hate to use wetsuits. I guess that is a lot off track from the thread, sorry. What readings were you getting by the way? Steve.

04/04/2004, 09:35 PM
"What readings were you getting by the way? Steve."

Incorrect readings ;) . AFAIK specific gravity and salinity correspond on a consistent scale so it's not an issue which is measured ? The idea is to let members check and confirm their metering source to a known scale.


04/05/2004, 08:22 AM
Agu, I agree completely, stability and consitancy are what is needed in a reef tank. If you use the same hydrometer it should be the same each time, but if it is off youre defeating the purpose and stressing the corals. Was yours off by hundreds or thousands or ten thousands? I have seen the plastic swing arm types off by several ten thousandths but not hundredths. The first number to the right of the decimal is tenths, the second is hundredths, the third is thousandths, the fourth is ten thousandths. The fourth number is usually where I have seen a difference. Such as 1.0255 to 1.0259, which is not much. Do the refractometers read salinity in 35 -36 or like SG 1.025? Also do they read all metal salts or just sodium chloride? Steve.

04/05/2004, 09:10 AM
I was just asking about the salts tested(I assume it is all salts) because unless people are checking calcium, magnesium, alk, and other metal salts, they could be way out of whack, just reading salinity or SG. I have seen people put a teaspoon full of this salt and one of that salt, in their aquarium daily and just check SG, which should go up with daily salt additions. Or not check and just keep it topped up to a certain level. I agree they are not exact at all. Steve.

04/06/2004, 09:56 PM
Can you calibrate a refractometer with RODI drops?