The 406 is rated for a 100 gallon tank, so may I assume you will be removing both eventually, once the Beneficial Bacteria gets established? The AC70 is rated for up to 300 gph, the 350 for 350 gph (together, that is some SERIOUS filtration
). Aesthetically, I like the AC since it looks a little more compact and modern. I dont have a real complaint about the 350 other than it just looks bulky and the one on my son's tank seems pretty noisy. The results are fabulous though on his 55.
You have a couple of options here for the changeover. You can leave both running until your bb gets established in the canister, then remove one or both of the hob's or you can remove one and run the other along with the 406 until you are ready to remove the other if that is your plan. Either way, I would leave at least one running for a month minimum to make sure your bb gets started inside the canister.
When you clean the canister, only clean one half at a time. That way you know you will still have the bb available. I had my wife make a little item from plastic canvas with an L on top and an upside down R on the bottom. She attached a piece of velcro to it and the other half of the velcro to the canister. When I clean the filter, I clean the side that is facing upwards and then turn the plastic canvas piece over so I know which side to clean next time.
PWC's are never a bad idea. Your bacteria is not in the water column itself but in the filter media, substrate and decorations.
When you get the 406, a video should be included with it. If you are not familiar with canisters (or even if you are) I recommend you view the video several times before you start setting it up. Follow along in the instruction book at the same time. Do the same for the first few cleanings to make sure you get everything back together properly. Most complaints about these filters seem to be based on leaks, usually around the seals. My bet would be improper installation in the majority of these cases.
When you start to set up the filter, play the video as you go, pausing at each step until you have completed the setup. Pay particular attention to the seals. Use petroleum jelly to lightly coat the rubber seal during assembly to help keep it moist plus keeping it from rolling out of the groove causing a cut seal and the inevitable leak.
Speaking of which, I set my 305 up sitting in a 4-inch deep plastic tub in case I did something wrong and a leak occurred. That keeps any water from damaging the floor, stand, carpet or whatever else might get wet.
Let us know how it turns out!
