Tony,
I noticed no other problems in the tanks, though they were only set up for less than a year. I would suspect older tanks might experience some problems other than low pH, but would not begin to guess what these might be.
The funny thing now, after living with fresh air coming in during the winter, is that I can tell if the condo is stuffy and that the windows need to be open more.
The weather is unseasonably spring-like here lately, so we often open the door to the balcony for awhile a couple of times during the day and evening to exchange the air.
Here is an pic of our old tanks and our dining/living rooms:
Should probably get a new pic, huh?