Nitric & Sulfuric acid

I was wondering if nitric acid is a biproduct of the nitrification
cycle or other chemical processes in the aquarium? The pH in
my aquariums is quite low; lower than can be accounted for by
CO2 injection. I wondered if this was due to humic acids or
from the nitrification process. A much stronger acid, sulfuric
acid, could that also result from the decay of organic material?

How does one obtain long term pH stability in those aquarium systems
where water is not changed regularly?

Steve Pushak     spush at hcsd_hac.com      Vancouver BC Canada