I have used this exact design in the past, it worked well but there were a few problems I ran into. 1st becareful putting Kalk in a plastic container over your tank... I've had a number of milk jugs burst open on me when using them for kalk. Its high PH will make plastic brittle over time. The container store has glass 1 gallon jugs. 2nd I could never keep the air-tight seal and I would end up draining the entire container of Kalk all at one time. If you choose to go with a glass jug you can get a rubber stopper to create a better seal.... Other than that it worked like a charm, Cool design