Ok, i'm not sure how many filers you are looping through but here's a suggestion
If you are using a csv or txt file import there are different ways to do it
Also, if you don't need credential and are using RPC it's easier as well
So for example
$filers = gc c:\filers.txt
$filers | % {
$filer = $_
$c = connect-nacontroller $filer
get-naaggr
}
Obviously, there are other ways to do that..
If you want to append it to a csv, I would suggest outputing it to a csv with -append and building an expression statement with Select-object for your controller
So, something like this.
get-naaggr | Select @{n='filer';E={($global:currentnacontroller).name}},Name, State,Totalsize,Used,Available | epcsv -append c:\temp\filers.csv -notypeinformation
Now once you use that type of select object, you will have to build expression statements with convertto-formattednumber or math .net functions
Give it a shot, if you get stuck we can help