Best place for your tank?

[Jexnell]

As far as placement goes it's better to place the tank across several floor joist rather just on one.
Using this as a reference. You want the tank to spam across several joist not along a single one to spread the weight out.

 

[Jexnell]

To find the direction they are going is pretty easy. For the ground, go outside and with a bright flashlight look into those vents placed every 10ft or so.

The second floor normally runs the same way, but could go the other. If you have a stud finder or the old fashioned way of using a hammer and the Mark1 eardrum to listen as you tap the floors. Solid thuds means joist hollow is not.

 

[twentyleagues]

I agree with what was posted before that ich is a parasite that is brought into our systems on a fish or other animal that is infected or just carrying it. Ich can remain dorment for months waiting for a host or waiting for the hosts immune system to drop enough to be able to infect it. Without treatment it will just wait it out. In this hibernation phase its impossible to detect and near impossible to kill, things like bleach will kill it.

It is possible if the fish are stressed in a location its immune system can become compromised and ich could take hold. Some fish are really interactive and look for people to "watch" while other will hide and try and scatter. Good call on the dpf Deadliestviper7 they are pretty much the eaisest puffers to take care of and in a 55 if it's the 4' version you could get quiet a few of those cute little suckers! They will look to find you eventually also so pitting them in an area of high traffic should not be an issue if you wanted. Tankmates will probably not be an option as with most puffers though.