Is this one of those things that can cause snail shells to turn white
and pitted? (LIVE snails, even...)

Hmm. Usually white and pitted shells mean low pH.

I have 80w over 55g (no CO2), so not even 2 wpg, but my pH is close to 8
most of the time. I have lots of vals, hornwort and some anacharis in
there, along with some crypts and a melon sword. Can the mix of plants
do the same 'damage' - stripping out CO2 - even without lots of light?

I suppose it's possible, but do you know your water parameters? What is your
kH? A pH of 8 might be normal for you.

Ordinarily, I wouldn't expect it to be a problem in a low light tank, at least
as long as there's reasonable aeration and regular water changes.


Leigh

http://www.fortunecity.com/lavender/halloween/881/