In a properly balanced system, the ammonia level should always be 0.0
Mardel sells a very accurate sensor that will allow you to monitor free ammonia at all times.
http://www.petsmart.com/product/index.jsp?productId=2753388&cp=2767036.2769160
It's other things that need to be considered when it comes to water changes, such as pH, GH, KH, TDS, DOC's, etc. Think osmoregulatory stress, having an isotonic balance from one week to the next...... not ima post my ammonia levels after i come back from my lfs.
Perhaps instead of spending so much effort & time on purchasing every CA species out there, focus more time on learning & understanding some of the basics.
sorry but i learned from this website that ph doesnt matter so i guess they are right when they say dont listen and trust everybody cuz form my understanding as long as you do constant waterchanges with a shedule your water is good as long as ammonia levels are good,and that ph doesnt matter but thats just the stuff i learned over time from this site
but now that you mention it i have the exact same product in the link u posted i have the ph one and nh3 so ima start using them in my tank and where is the best place to put them midlevel tank or near top of the tank water for best results
also i went to my lfs and they said my water is good and that ph was good, ammonia good, nitrite and nitrate good , i didnt ask them for exact numbers because they would say if someting is bad and i bought maracyn 2 because it sounded better for what my umbee has