Hi Shango, It may be a combination of the increase in CO2 and the water change. If you increased the amount of CO2 going into the tank, that would have reduced the amount of dissolved oxygen. The colder water we have in our water systems during the winter will have lower dissolved gas (including oxygen) content. When you removed the aquarium water and added the tap water that may have reduced the oxygen as well. What you are seeing may be a combination of the two. I agree that adding an airstone and increasing the water circulation, and possibly dropping the CO2 back down, may be the best way to revive your Ancistrous. Roy _______________________________________________ GSAS-Member mailing list GSAS-Member@thekrib.com http://lists.thekrib.com/mailman/listinfo/gsas-member