Amount of salt for 3-5 gallons

Interesting. So let me see if I get it: if DEmich were to add 35 g of his salt mix to about 750 ml distilled water, stirred for a bit, then topped the container off at 1L, he'd be close?
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Ha! I hadn't even realized that I was getting close to the value being discussed, I was just going from a rough estimate on the calculator! I was on coffee #1 at the time, so I wasn't thinking, but yeah, obviously "marine" tanks would be seeking near-ocean values. So yeah, he'd probably be dead on. About 35g/L for ocean water.
 
You cannot hope for any degree of accuracy using either either weight or volume except for the first time the package is opened. Marine mix is highly hydroscopic and will take up water from the air once it is opened. This increases the weight, so that scale use will no longer be accurate. It also clumps the mixture, so it will be lumpy rather than a smooth and fairly uniform powder, which distorts the volume in a measuring cup.

If you are using small quantity, buy the 5 gallon box and dissolve it in a 5 gallon tank in about 4 gallons of water. then you have predissolved SW of easily measured specific gravity whenever it is needed.. With an intact coverglass the evaporation rate will be trivial,and a specific gravity check prior to use will allow dilution if needed.

IMHO & IME, life is so much easier and simpler with predissolved mix waiting for use on the shelf. The mix does not dissolve instantly in any case, I never use before 48-72 hours anyway. Salt water setups are expensive, operating costs are high, the critters are expensive. A weekend sale tank at the chains and a powerhead and coverglass are relatively cheap.

FWIW, YMMV.
 
In the end, I would never put ASW into the tank that I haven't tested with a hydrometer that's been calibrated with a refractometer. I thought the post was about getting oneself close to the mark.
 
Hey, I was just answering a question about SG and salt content. I don't claim to know anything about Marine setups or reef aquariums. I may do the oceanography thing, but when I get home after work, I'm purely freshwater.

RTR is right, the pure salt is stringly hydroscopic. However, this will get you close to the mark and that may be good enough. You may just want to err to the side of a little extra to account for the water, I don't think that small changes in salinity would have much effect, and we are talking very small volumes here, so it would be significantly diluted when added to the tank. BUT, I do not keep or have any experience with marine aquaria, so I really don't know.

Bottom line, if you have a reef/marine setup, you're gonna need a refractometer (or hey, if you can afford a conductivity probe...), so you're gonna be measuring anyway, as mogurnda says.
 
Bravo!

Thank you, one and all. I sort of expected prolific responses, my expectations were pleasantly exceeded :D

Also: Thanks, Andy16, for permitting this use of your thread :)

Now to go price refractometers...;)
 
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