Prime is reasonably priced, and a little goes a very long way. I have always read the recommendation to dose the entire tank. On my 300 gallon tank, that equates to three capfuls. The gallon of Prime I have has lasted for years. It's been seven years since I've used a Python, but when we did, it was very easy--we just added the Prime where the water was streaming back into the tank when we refilled via the Python. There was no doubt in my mind that the Prime was getting mixed. Now, we have such a strong current in our 300 gallon tank, that we just dump the Prime any where in the tank. We pump the water back in via a Hammerhead pump, and the water is turbulent. I just don't dump it on one of the fish.