Trop, this is how I route water when things do not work out as planned. I use a bit of silicone and a few rocks and sand, or even pits of moss covered wood to "adjust" the flow.

Another trick I use is to do a "dry" run , with water before adding anything else to the tank. I like to use small slabs of foam with some velcro strips, straight pins or poster putty (depending on which construction method I use) to make any needed adjustments. A drop or two of food coloring to the water helps in spotting where the issues arise at.