New hydrometer for saltwater tank. Links included. Any experiences?

Question

I always used a floating glass tube hydrometer/thermometer combo. This link is similar to the one I'd been using.
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=7360&Ntt=hydrometer&Ntk=All&Ntx=mode+matchallpartial&Np=1&pc=1&N=2004&Nty=1
But today, I broke my 4th one in 2 years. Yes, I'm clumsy. The local pet store, which definately doesn't specialize in fish, only has this Instant Ocean hydrometer:
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=4952&Ntt=hydrometer&Ntk=All&Ntx=mode+matchallpartial&Np=1&pc=1&N=0&Nty=1
I've never used these before or known anyone to use them, but I was in the middle of a water change and needed something fast. It seemed to give readings that were different than the floating one. So which one should I trust? Any experiences with this Instant Ocean hydrometer?

Answer 1

I've had a few experiences with them and it seems difficult to get consistent readings with them. I'd try soaking it a while and then tapping it to get all the bubbles off and I'd get 3 readings on three consecutive measurements.

Personally, I liked the old models of their SeaTesT hydrometers (just a plastic square with a swing arm inside), instead of the different shape they're using now. I've tried the Instant Ocean, Deep Six, and Red Sea and they're all about the same. And I don't like the "ideal range" on the scale most of these use - it's not in the range for inverts, only fish.

Have to warn you though Chris - the plastic ones break too! I've broken my share of each.

Answer 2

The swing arm type hydrometers can be inaccurate and also lose accuracy with age. I would recommend using 2 and comparing results and changing them every 6 months. I have found some swing arm types to be .004 off brand new. May sound a little overprotective but I have seen an entire tank wiped out by an old hydrometer. The guy lost everything.

Make sure you rise it well in freshwater after each use and make sure there are no bubbles at all on the arm when testing. Any salt film left on it or bubbles on the arm can change the reading dramatically.

A refractometer is the most accurate. drfostersmith has them for roughly $40 I believe. Used to you couldn't get one less than $100. They are a good deal as you will spend more on the swing arm types in the long run.

Answer 3

I have the same one you posted the link to and havent had any issues at all. I usually just tap it a few times to get an accurate reading. I have tried different ones to make sure I am getting a correct reading and it works everytime. I have never broken it and it seems to be holding up well. I am sure you know this but I will throw it out anyway ,maybe someone reading this doesnt. ALWAYS rinse with fresh water and shake. I usually run tap water over and through it for a good 30 seconds. If you just empty it out, some small salt particles will stay attached to the hydrometer and the needle inserts and eventually start causing problems and false readings. I would go with the one you are looking at. Good luck.

Answer 4

I have used that exact model and have several at work. I agree that they aren't always as accurate as floating hydrometers. One thing I find that you must watch is any bubbles, no matter how small on the swing arm will throw off readings and it seem to accumulate them more easily than glass floating styles. If I had different readings from the same tank on those two items, I would trust the floating style first. If you really want accurate here's my suggestion for your list for Santa, it's worth every penny and very accurate:
http://www.marinedepot.com/md_viewItem.asp?idproduct=AM1115

Hope that helps

MM