You will probably have to cycle the tank again. The bacteria needed for a healthy tank lives in the filer media and gravel ect, once that has been rinsed the bacteria die. The bacterias needed are living so also need well oxygenated water to live and many things can kill them off eg using cold water in a warm water tank when changing water, not using a chlorine remover before adding new water.
It normally takes between 4-8 weeks to cycle a tank fully depending on the temp and other things.
Now for the -*test*-('") kits, when you add fresh water (fill the tank again) you should have 0 readings of ammonia, nitrite and nitrate. If you are going to cycle with fish (which most recomend fishless cycling) the ammonia will build up first and will get really high (and possibly kill your fish) this is when the ammonia -*test*-('") kit comes in. Test the water everyday once ammonia is showing and do water changes before it gets really high (about 20%) then also start -*test*-('")ing for nitrite (they will come next) the nitrite levels should get higher and the ammonia should lower. It should be noted that nitrites are still toxic to fish in high levels so watch them closely once again do water changes when neccesary. Now comes the nitrates now anything under 40ppm (preferably 20ppm) is ok, but if it gets higher than this it can cause problems also. once there are 0 readings of ammonia and nitrites your tank has cycled.
Nitrates need to be removed by doing regular water changes, if you have a planted aquarium then the plands do use some of it but you still need to do water changes ect.
NB - dont vacuum while the tank is cycling, the bacteria need to set up a stable home in the gravel and if you vacuum you can upset the cycling.
Once the tank is cycled you should only need to -*test*-('") for ammonia, nitrites and nitrates if you fish are acting unusual and you have a feeling something is wrong.
Hope this has helped

Fishfriend