hi, and welcome to the forum! i'm sure you'll find a ton of useful information here that will hopefully make the fishkeeping experience worth it.
first, some questions...do you currently have fish in the tank? how many and what kind? if you do not have fish, your nitrite reading should be 0.
next, what size tank is it? does it have a heater and what type of filtration? i'm sure the pet store went over all of this with you, but it's good for us to know.
now, for a little advice, first i'll direct you to some of our "pinned topics." these contain some great information written by fellow forum members...they contain some information that is absolutely necessary before dealing with your local fish store (you will see it abbreviated "lfs" a lot here) next.
first, read this..
http
/www.fishforums.net/index.php?showtopic=10099
next, some useful rules
http
/www.fishforums.net/index.php?showtopic=6756
more great info..
http
/www.fishforums.net/index.php?showtopic=13133
as for stocking your tank, unfortunately guppies and neons may not be good choices..neons are known as one of the least hardy fish out there and will mos tlikely die due to the cycling process....also many strains of guppies are not hardy as well.
if you don't have fish in there now, you could always try to do a "fishless cycle"...see information below..
http
/www.fishforums.net/index.php?showtopic=73365
i know that is a lot of information to read and all, but just browse through it...if you have any questions feel free to ask! and enjoy your stay!
