If your water comes from a well, you can probably add it immediately without adding any conditioners. If you have metals in the water, you may need to condition it first. If the water is similar in temperature, then add it right away. If you have city water, you probably have chlorine and chloramines in it which will require the water conditioner also. Also check to see if you have a significant ph change in your water by placing a bowl of water straight from the tap out overnight. Test the ph when you first fill the bowl, and then check it again in 24 hours. If there is more than a .2 difference in ph, you will have to age your water so it doesn't hurt your fish. You do this by placing conditioned (if necessary) water in a bucket or barrel with a good airstone or powerhead that causes a lot of movement. This will allow it to gas out, and your ph will consistent to the ph in the tank.