adding carbon dioxide

[Charlotte Seibert]

  I read adding carbon dioxide lowers PH, but could also increase alge...two questions..how do you add the carbon dioxide and what do you do to lower the chances of alge other than keep as much sun out as you can?  I just recently cycled and sure don't want alge bringing up that ammonia I worried so much about.

[TCLynx]

right when we say cycled we are talking about the bio-filter being cycled up to the fish load.  Simply having 0 ammonia and 0 nitrite only constitutes cycled if you are able to feed your fish the right amount daily or as Vlad notes for fishless cycling you can dose the ammonia to a certain point and have both ammonia and nitrite back to 0 in 24 hours.

The nitrification process is naturally acidifying so usually once a system is cycled up the pH will start to fall and may even require buffering.

However, there are other things that can affect pH.  Primary ones of concern are the source water (like hard well or tap water might keep pH really high) or the media (if there is limestone, marble, shells or other calcium carbonate heavy materials in your media the pH will stay high.)

Expanded products will often have an alkali effect at first but hopefully short term from the dust residues on the expanded shale or clay or slate from the kin process. 

Generally as the system gains maturity the pH will fall.  It is usually best to avoid adding anything directly to a system with plants, bacteria or fish that will lower it's pH drastically.  If you must use acid to change the pH, it is best done to a separate container of top up water and allow it to stabilize before adding to the system.