I am in the process of building a gravity-fed HERMS system out of metal shelving. However, I am concerned ablut the fsct that I have different sized tubing at different stages of the system. From the mash tun, I am using 3/8" tubing, while the HERMS coil uses 5/16". However, the tubing to the pump is 1/2". I am using the correct barbed hose fittings so I dont need to worry about leakage. What I am concerned about is oxygen exposure in the lines because of the changes in tube size between stages. Is this a problem? Thanks!