Hydrometer accuracy

[Nugg]

Hi all...

I thought I would start this post off with something different by saying that my reef is actually doing amazingly well and has been for a quite a while now, thanks in no small part to what I've learned since being a member of this board. The only "problem" is my colt coral totally dominates the left side of my tank. I guess it's pretty happy.

But I do have a question here. How accurate are the standard SeaTest plastic hydrometers? I've heard that they're usually a couple of tenths off on the low side. Accordingly, I keep my salinity at 1.023 according to the SeaTest, thinking it's probably more like 1.025 or 1.026.

Am I right or wrong on this? And what is the most accurate way of testing salinity?

Thanks,
Jeff

[FishDaddy]

Hi Nugg,
Glad your tank is doing well!
I've had a couple of the SeaTest plastic boxes, in fact still use one to get my salt mix close and then fine tune it with my Tropic Marin Floating glass hydrometer. My Seatest reads a full 0.001 lower than the Tropic Marin. The SeaTest is also susceptible to false high readings if there are any tiny bubbles stuck on the swing arm.
I like the Tropic Marin but it does require sufficient depth to float and taking a good reading in the tank requires turning the pumps off. Some use a tall cylinder to test with the TM.

The best method is to use a refractometer. I plan to get one but that's another one of those many, many items on a big list of things to buy for my reef!
Dick

[Rick O]

Hi Nugg.

I still use the cheap plastic box. As Fishdaddy says, you have to get all the bubbles off the swing arm. I compared mine to an electronic monitor (forgot the brand) at the LFS and was surprised to find that it was fairly close. I try to keep my salinity somewhere in the middle of what I consider to be the acceptable range so that any variations from accuracy will still be tolerable by the inhabitants.

If your fish and corals seem to be happy and doing well then I would just go with what you've been doing.

Rick

[Pik]

Nugg,

I think it depends on individual hydrometer too. Some may work perfectly, some may be as much as .004 off. The best thing to do... if you know someone who has a Refractometer or one of the tropic marin hydrometer, test yours against that.

Pik

[Nugg]

Cool, thanks guys. Everything in my tank is flourishing so I guess my salinity is fine. Can't think of anyone who'd have a refrectometer to check against anyway...

[bill-e]

How bout as much as .006

There's a good article at the following url, unfortunately the links to the pics are broken, but read the text, you'll get the picture. Spend 15 bucks and buy either a Tropic Marin or Marine Enterprises glass hydro from Premium Aquatics.

Your tank may look great now (and I can sympathise with you regarding the colt) but the more you use the plastic hydro, the mor inaccurate it will become, then one day the tank wont look so nice and you'll wonder why.

Either glass hydro I mentiond will be plenty good for your purposes, and other than not dropping them, the only maintenance is a vinegar soak every once in a while.

http://www.harboraquatics.com/hydrotest.html

[Doug1]

I use the swing arm SeaTest but double check it against my Tropmarin at least weekly and use it as final arbiter when making up new water. Mine seems consistantly .002 higher than the Tm Hydrometer, even after rinsing it out in RO water and storing it upside down

[Nugg]

Bill, thanks for that article. I'm definitely gonna buy a Tropic Marin tomorrow...