Which refractometer?

[SpyC]

Mercury? Not in mine.. Those bits at the bottom are made of lead (at worst) but also possibly simple iron beads.
I turn off all pumps - put the hydrometer in the tank for 10 seconds, observe where the readings are and job done!

I had read elsewhere mercury was in it. The beads are just weights and not where I would expect mercury to be. Maybe the posts I saw regarding mercury had this confused with older thermoeters.

 

[Borat]

I had read elsewhere mercury was in it. The beads are just weights and not where I would expect mercury to be. Maybe the posts I saw regarding mercury had this confused with older thermoeters.

Mercury would serve no purpose here - perhaps as you said you got confused about some other thermometer conversation.

Cheers,

Borat.

 

[Arkayology]

I got a Milwaukee digital refractometer open-box from one of the major online retailers for $60. I like it a lot and is in line with my BRS refractometer.

 

[that_boy_fini]

Milwaukee is 110 on Amazon my lfs matched the price I legit love this thing

 

[DaprDon]

Mercury? Not in mine.. Those bits at the bottom are made of lead (at worst) but also possibly simple iron beads.
I turn off all pumps - put the hydrometer in the tank for 10 seconds, observe where the readings are and job done!

Same here! The only draw back you would need the cylinder for if if you're mixing 2gal of water in a bucket. It's too long to test that.

 

[Borat]

Same here! The only draw back you would need the cylinder for if if you're mixing 2gal of water in a bucket. It's too long to test that.

You are doing something suboptimal.. Unless your are changing something like 50% of water in your tank, your salinity management should be as follows:
- work out (once ) roughly how much salt (by weight) you need to add to a fixed amount of water (this is your bucket that you always use) to get to approximately correct salinity. For example I add 900 g to 25L of RO (for the last 4 years) and I never have to do any salinity corrections when I do 12% WC.
- perform your water change (with water that's been pre-mixed to your rough calculations), wait for 5 min and measure the salinity of water in tank. If it's a tad low, just add a bit of salt to the sump. If it's too high - just remove a bit of water (RO top-off will compensate for that).
- job done.

Here's the maths behind above: let's say that you do 10% WC. Let's suppose that your approximate salt mix is "a bit" wrong, say it's 40ppt (instead of 35ppt needed). Then upon mixing your tank water of 35ppt and new water of 40ppt you would get a mix 0.9*35+0.1*40=35.5ppt.. So even though you added a water that has a lot more salinity than needed- just because you added a relatively small fraction, your overall change in salinity is small (35ppt -> 35.5ppt).

Small salinity changes for a short period of time have no impact even on delicate corals. Even significant salinity changes over long period also don't have significant impact on corals - unless you go way off safe bounds.