New Tanks Questions (Try again)

I set up my first tank about 2 months ago, and everything is going
well at the moment. I've got a 30gl tank with 10 neon's, 8 bleeding
hearts and 2 albino catfish (oh and a couple of shrimps). I got a few
questions though about feeding and water conditions.

Firstly i'm starting to use R0 water from my local dealer for water
changes, now how often should i change the water and how much should i
change. I've recently read a book which suggested changing 20% a week,
but my local dealer told me I'd only need to change about 10% every
5-6 weeks or so. I've been doing the later, about 20% a week. Also, R0
water, what exactly is it and why is it better than normal water.

Secondly, now i've got some bottom feeders, (the albinos), do i need
to substitute their diet with any thing. I'm currently feeding flakes
and now and again frozen live food, and also live food. I'm also
interested in getting some redtail corys today so will i need to get
some different food fo them? I've checked my ph which is 7.6, no
ammonia, no nitrites, kh is looking good now. Any comments would be
welcome.

Thanks