Unless the pet store you are going to is using a liquid test kit and giving you specific numbers, then stop relying on them. What Nick is asking is the hardness of your water. Is it soft or hard water? You can find this out by looking on the website of your local water authority.
I would also suggest purchasing your own liquid test kit as being able to get quick results for water parameters are key to maintaining a tank and diagnosing what may be wrong with the water quality should something go south (sudden fish death, flashing, lethargy, any odd and sudden changes of behavior are warning signs of spikes in water parameters). I use an API freshwater master test kit, you can purchase if for 30 odd something dollars (in the USA) at petsmart/petco and about the same online. It's 30$ but you get hundreds of tests out of it, vs spending 8 dollars on a box of test strips and getting only 8-15 tests (depending on the brand you buy).
We need to know the water quality because some fish thrive in hard water, like live bearing mollies, platies, and guppies. Others thrive in soft water, like corydora and angelfish. We will only make suggestions once we are informed of your water resource and the tank you plan to house them in, as any responsible person in the hobby puts the well being of said fish above all else.