Many members on here have FX5s on 55g tanks without problems, and most of us have excessive filtration no matter what size tank we have. I don't think it will be an issue, and you can always adjust the direction of the output if you think it's too strong. As far as cleaning the tank, just clean it well enough to get rid of the salt/mineral deposits, and give it a good rinse. Water and vinegar works well for this. You can wipe down/soak everything in a 10:1 (water:bleach) solution if you are concerned about some pathogen surviving in the tank.