Thanks for sharing the photos. That tank is great.
Had thought about this being a potential problem but I've been using them in 20Ls for about a year and with a quick cleaning every 3-4 months, I haven't had much of an issue. Though, honestly, I tend to clean tubing that's visible every week if it's needed.
I would try to avoid a spray bar the length of the tank, I had this on my 12 gallon long and i eventually ended up with a clear acrylic tube that looked like this