I will be using an elevated container attached to tubing with a ball valve on the end to drip a liquid into my saltwater aquarium to help with coral growth. Conceptually it will be similar to an IV drip but just homemade. Ideally, I want to keep that rate of flow as constant as possible as the liquid in the container drains over time. It makes sense to me as the liquid gets lower the flow rate will decrease (at least in the IV type setup). Another way I could do it is to drip a hole in the top of the container and place the tube so that it creates a siphon. Would this still be prone to that decrease in flow over time?
Here is a trick to get what you want.
Suspend the reservoir with a spring that pulls the reservoir higher as the liquid drips out of it. By scaling the spring constant and the proportions of the container, you can get the reservoir to rise exactly in lockstep with the drip rate and thereby hold the source pressure for the drip line constant.