Bgreazy,
What he said!
I think you should read your books again. a hydrometer is a rectangular box type thing with numbers on it and a swing arm. This will give you your salinity or specific gravity. I have not heard of anyone making one but there are some pretty good DIY people here.
You should "understand" what your reading and if you have questions you can certainly ask questions here.
That post up there really sounded like you have never read a book and your jumping into this hobby a bit too quickly. You should at least be familiar with the basics, like your question "how do I know how salty it is'?
Also, different kinds of tanks, fish and corals, are cared for differently. You should also read up on lighting. If your gonna have any coral in there.
lastly, if your starting with a 5 gallon, your water perameters can and will change quickly. actually the larger tank the better with salt water. (at least until you have experience)
The question you asked about throwing in the rock and waiting about a month sounds "fishy too". If you mean if that it's alright to add fish then, well answer is .. YOU HAVE to make sure your TANK IS COMPLETELY FINISHED CYCLING" and the way you will know this is by buying a test kit and testing the water . you have to watch the ammonia go up, the nitrites go up and then watch them go down to nothing... then you should be watching your nitrates becuase they come next. It's called "cycling" your tank. VERY IMPORTANT!
Hope this helps... good luck, Kim
P.s. I bought "saltwater tanks for dummies", it was pretty informative. You should also pick up maybe a fish guide, it will tell all about the different fish and their care and compatability.
