If you add the conditioner to the tank after you are done you have to dose for the whole tank. Thats why I don't use the python when filling my tanks back up. I use prime for my conditioner and use a 4 gallon bucket. I put 8 drops from a eye dropper in the bucket put it in the bathtub and fill it up and the water stirs the prime up. If I waited until the tank was full I would have to add enough for 150 gallons instead of whatever I add say 30 gallons.