That noise is the integrated bubble counter (bubbles hitting impeller). :icon_coolWorks great for me. I have an AC20 powerhead in my 29g with the CO2 line hooked directly into it. Makes a nice mist, though it is the loudest thing in the tank. Still not loud enough to cause me problems but if you have a dead silent room you will hear it.
From my experience it uses up more CO2 than say using a Rex reactor, but the plants like this method of diffusion better. The fish will also thank you for not killing them. Misting from a powerhead causes less stress on the fish because not all the CO2 gets dissolved directly into the water.
This is "my" logic since I'm no expert, do take it with a grain of salt if you will. When "misting" from a powerhead you create a gazillion tiny bubbles that will adhere to the plant leaves, disperse at the water surface, and dissolve in the water. Note - not all the CO2 gas is 100% dissolved in the water with this method.When you say "more" co2, are you meaning several more bps? I have used 3 bps in a 46 gallon bowfront when using an external PVC reactor and when using the water pump. The water pump output is about 2 inches from the substrate. It sits in the left rear corner and aimed toward the front glass so it causes a current going in a counter clockwise direction toward the canister intake in the right rear corner. The canister output is mid way up in the left rear corner aimed at the front glass creating just enough turbulance at the surface to minimize surface scum.
The reason I went through this boring explanation is that there are numerous reasons on needing more co2 bps for a given co2 concentration. An example would be, you had minimal surface turbulence when using the reactor because of restricted flow. Then you added the powerhead creating more surface turbulence, causing more co2 loss.
Just seeing if there might be something I'm missing in my observations.