when setting up a new aquarium what chemicals should i purchase to treat the water before adding fis

I am setting up a new aquarium for my son and need to know what to buy to pretreat the water and what to treat the water with after fish are in-during water changes. We have tap water and in our other tank have been loosing our guppies left and right, however our black moor seems fine

If this has already been answered, then please forgive me, but really the only chem you should look to use to start off a new tank would be water conditioner. This and only this (because if you are using tap water it will most likely have Chlorine in it, as well as other potential Chlorimine elements and other hard elements).

If you have a water purifier as I do - then all you need to do is fill it up, and cycle away (and may I make a suggestion? If you do this it will not only take less time, but it will also be less messy). Do a fishless cycle. If you have old media filters from a disease free tank then you could use that to seed the tank, but it is not absolutely necessary. With that being said - get some clear/pure Ammonia from one of the lower grade Grocery Stores in your area (like a farmer's market or something similar), and look for plan ol' No-Name brand Ammonia (that has no fragrances or surficants in it). The way to tell is to look at the ingredients, or simply shake it up (if you get foam - put it back and look for one that only provides air bubbles when shaken at the top of the bottle).

I'll stop my babbling - check out this site as it's an awesome resource on fishless cycling!