If _FiltrationString is an NSString you should be using this command:
_FiltrationString = [NSString stringWithFormat:@"%@",[alertView textFieldAtIndex:0].text];
[_tankFilterArray addObject:_FiltrationString];
instead of
_FiltrationString = [alertView textFieldAtIndex:0].text;
The command equates _FiltrationString to the address of the alert view textfield.