Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Tap water high pH = low CO2
Aging it, lower pH = it is gaining CO2 from the air.
To off gas the gas in the tap water, or to incorporate more CO2 faster:
Set up a bucket of water with any sort of pump or bubbler.
If you use a fountain pump set it at the bottom middle so the water shoots up through the bucket, then sheets out toward the sides. This pattern is called a flume. By exposing the water to the air and circulating it you are making it do the gas exchange faster.
You can also incorporate any other water treatment and be sure it is well blended. For example: Are you keeping black water fish? Add a nylon stocking with some peat moss.
Are you adding Excel or related product?
You could try adding it via syringe, aimed right at the BBA. Do not overdose, use just the labeled amount, but aimed right at the algae will create a temporary very high level locally, and will start killing the algae. Turn off any water circulation (pumps, filters...) so the concentration stays there for up to half an hour.