Hydrometer issues...

palmer

palmer

Member
Just a word on hydrometers...I'm not going to name any brands here but...I had one of the plastic fill with water types that was reading way too high. The hydrometer was reading .027 but when I used an optical model and an electric probe ($500 model from the lab where I work) they both read about .034. I then used the same three hydrometers on a friend's tank and got the same margin of error. Then used the same brand plastic hydrometer, but a differebt one, and got not as high of a margin of error but it was still reading about .004 too high. I know they have to be seasoned before use, which they were, and they are not highly accurate to begin with, and they probably work fine for most people, but I'm just throwing this out there as more credence to ...You get what you pay for. I'm wondering if this was the reason that my zo's were not opening some time ago, the salintiy may have been too high, not too low.
 
jumpfrog

jumpfrog

Active Member
You're right, it's hard to rely on any of the plastic ones. I think for something as important as salinity, paying 50 - 100 dollars for a refractometer is a great investment.
Certainly gives me some peace of mind.
 
murph

murph

Active Member
Thats pretty much what I do Mud. I have a trusted LFS test my water with his refractometer at least once a month to make sure my hydrometer which reads .05 low is at least "consistently" wrong. Its then just a matter of some simple math to make the adjustment for SG.
I had run my tank for the first 5 months or so at an SG I thought was 1.025. The day I went to buy my first coral I took a water sample with me to the LFS just for yucks thinking I had everything right and ready. Unfortunately I went home that day without my first coral to spend a week bringing my SG down from 1.030.
I probably wasted a whole bag of salt mix in those first months mixing batches way to high. At least the aquarium Gods were looking out for me or at least that first coral as it probably would not have enjoyed life in my tank prior to the SG adjustment.
 
chipmaker

chipmaker

Active Member
Even with a known good swing arm type hydrometer its still easy to get erroneous readings. Just a tiny air bubble on the arm or having it setting just slightly off level gives eroneous results, and then the temp compensation. I have been told they are cal'd for the most opart to read SG in the rage a tank is kept, and if you do look at the figures with temp compensation, SG is not all that much of a difference in readings at say 78 a it is at 80. Its just too much hassle to fool with a device you need to dip and empty and bump and fiddle with to get a reading as compared to spenidng less than 50 bucks and getting a refractometer...Cal it with a little RODI water, and test with confidence your water is what the refractometer reads.....
 
mudplayerx

mudplayerx

Active Member
It is very easy to figure out the specific gravity of saltwater with different temperatures. There are graphs on the internet and in many aquarium books. You just test the water and find the column with your temperature and scroll down until you find your reading.
The swing arm hydrometers do tend to get bubbles attached to the arm, but a few taps cures the problem. If I had money for a refractometer I'd get one, but until then, ole betsy is doing a fine job.
 
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