Yes, they will lose water.
I like to keep some in mine to keep an eye on things so I do top them up but other people let them run dry when they are tuned in.
Fish will have <"different tolerances to high CO2">. Fish that come from running, or cooler water, will be less tolerant of high CO2.and my rainbow fish were all smimming at the surface as if trying to get air, but my apistos were just going around normal.
Hi all, Fish will have <"different tolerances to high CO2">. Fish that come from running, or cooler water, will be less tolerant of high CO2.
Because the haemoglobin in the blood transports both CO2 and oxygen, high levels of CO2 <"depress oxygen uptake by the gills">.
cheers Darrel