You have it reversed. Water should flow into the reactor from the top, and this should be about where the CO2 intake is also (maybe 3 inches below the top or so). Water should flow down the reactor and out the bottom to the main tank. This allows the reactor to work how it should: CO2 will flow into the reactor, and the bubbles will rise. The bubbles will continue to rise against the flow of the water, and when the CO2 is completely diffused into the water, it will be carried out the bottom of the reactor. If you set it up so that the water flows upwards, the bubbles will travel with the flow and you can get bubbles in your aquarium and very ineffective diffusion.
Also, I'll add that in your huge 340gallon tank, you might need 2 reactors and 2 CO2 input lines since it will be so hard to move the CO2 concentration up in that volume of water. It doesn't help that you also have a sump, which will offgas the CO2 faster than without a sump (sumps are normally great things for almost everything, but keeping CO2 up in the water is not one of those things).
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.