Well I just got done mixing my first batch of SW. I had been buying from the LFS but decided to start mixing my own. I'm using Tropic Marin Pro Reef.

I have a refractometer that is calibrated and a Coralife deep six hydrometer. The readings the two gave were extremely different. For my water I wanted the salinity to be 1.025. I added a 1/2 cup of salt per gallon, based on my findings on here. Long story short, my salt ratio is all messed up now due to the hydrometer being way off. When I finally got the water dialed in, the refractometer read 1.025 and the hydrometer read 1.020. To me that seems like a HUGE! difference.

So now next WC I will have to only use the refractometer and figure out exactly how much salt to mix.

Moral of the story, dont use a hydrometer for WC's if you have a refractometer handy. I guess I really could have screwed my tanks up if I would have used the very high salinity water that I started with.

Yup, learnt this the hard way. Crashed my first system exactly that way. Thought I was changing water to a specific gravity, but slowly I was increasing the salinity of my tank. Ended up killing nearly everything - even my dendros, before I could even get a clue to what the heck was going on.

Hydrometers shouldn't even be sold.

Refractometers should be THE FIRST thing you buy getting into the marine aquarium hobby.

so, what your saying is if the hydrometer says 1.020, its actually 1.025, gotcha....

havent bought a refracto in 10 years, probably not gonna anytime soon...maybe ill get one for xmas

i take my hydrometer to the LFS, measure some water, have them measure the same water with their refracto, do some complex math, BAM saved my self 40 bucks

so what you're saying if a bubble get stuck on the back of your hydro's needle and you don't notice, there goes your reef system. good thing you saved 40 bux

ive been doin this for a min, you dont leave it in the tank, you take it out, put it on a level surface, and make sure there isnt a bubble.....tap accordingly, buy beer with the 40 bucks i saved.....

Right, I was more inclined to someone looking at this thread for advice. I'm sure a salty vet could taste the water and know the SG level, whatever. best advice: get a refractometer

What did you use to calibrate the refractometer. Even refractometers have been known to be off from time to time and calibrating with RO/DI water isn't always accurate, either. I usually suggest buying calibration fluid and making your own to compare the results. They should essentially be the same.

dont take what im sayin as me downplayin how useful a refractometer is, a quality one is a great tool to have.

so what about the kid that buys the discount chinese hydrometer and gets the bunk one? all things can have flaws...

the quality of hydrometers is ALOT lower than with refractometers, each one measure diffrent, and if its reading is matched with a quality refractometer, you can get by with one....

i was pissed when i lost my old one, it was nice and reliable, had to take my chances with a new one....go all the way to the LFS and get my readings dialed in...

if money isnt an object, why not just get a conductivity meter? SO much easier than having to tap a hydrometer or squint into a refractometer

Same thing happened to me. My hydrometer reads a LOT higher than my refractometer. Can't believe I used it so long.

A glass hydrometer from a reliable brand should be as accurate as a refractometer (with ATC-automatic temperature correction). A conductivity meter is even more reliable.