If your tap water does not change in ph after a day or so when adding it to your tank water, just get it as close as you can to your tank temp, and add it to your tank using your aquasafe. Either pour it into a bucket first and add your aquasafe, or if you use a python, add the aquasafe as it's going into the tank. I think you can get buy with only using enough aquasafe to treat the amount of water you are adding back in, but you can't overdose on the aquasafe if you want to treat for the full amount of gallons in your tank. If you ph is more than .2 different than your tank water, you will have to "age" your water before adding it to your tank. To test this, get a bowl of water straight from the tap and test the ph. 24 hours later, check the ph again, and if it's more than .2 different, you simply put your water in a bucket with an airstone or powerhead for 24 hours to let it "gas out". You can put a heater in the bucket so it will be the same temp. as your tank, and simply add this water to the tank. Aquasafe will need to be added to this water also.