The question is basically in the title: how much salt must I add to a liter of tap water to match the salinity of a liter of ocean water? I know that salinity [probably] varies from place to place, so just pick one at random.
Seawater averages out to 3.5% salinity or 35/1000[sup]th [/sup]
So about 35 grams for a liter
Moderator Note
This was originally posted to another thread by mistake, since it was clearly a new topic. I have moved it to its own separate thread.
Was the post a bit too salty for that thread? 
And we might was well get this out of the way sooner rather than later, especially since What Exit gave a nice answer already: Which ocean?
I’m not sure if its that simple.
Tap water is already slightly saline. It can have over 1000 ppmof salt, or over 1g per litre.
If you add 35g of salt to 1 litre of pure water, you will have a solution of 35 grams in 1035. That’s about 3.38%
True enough but of course seawater is kind of an inexact measurement. I was basing it on saltwater fish tanks to be honest,
It’s not as simple setting up a marine tank as adding a bunch of table salt to tap water. This site shows all of the steps in doing so, and this page in particular recommends using deionized or RO purified fresh water and “synthetic ocean” salt. On Amazon, the two brands specifically mentioned are $50 and $57 respectively for 56 pounds, enough for 200 gallons. Smaller packages are available but as the page says, you’re going to need plenty of salt water for the initial fill and any water changes.
If you’re not considering a marine tank, eyeballing it with NaCl is good enough.
Why are you trying to do this? Seawater generally contains rather a lot beyond simple sodium chloride.
No reason at all, was just curious.
:dubious:
You’re not growing the creature from the black lagoon or anything like that, are you?