I have recently completed an ich regimen for my cardinals - a week at 86F and salt at 1 tbsp/5 gallons H20. During that time, the outflow was just on the surface of water, to allow for some surface agitation, due to the lower dissolved O2 as a result of the higher temp. I completed the treatment last Thursday, and have been doing daily H20 changes to bring the tank closer to 0 ppm NaCl (currently, estimate .11 tsp salt/gallon).
I have also slightly
increased the CO2 bubble rate, and lowered the outflow to below the water surface, to encourage a better dissolved CO2 - a recent outbreak of GSA, and plants were not pearling well enough, in my opinion. (I have a new fixture on board - 2x24W T5HO). Even though I've lowered the outflow, there is still a good amount of surface ripple - Fluval and Koralia nano in circuit flow, the Koralia close enough to the surface that the ripple almost breaks:
Fish did well during the ich treatment, and ate, behaved vigorously since - out and about.
Since this afternoon, though, they have been incognito - hiding together, low in the left rear of the tank, in a dense forest of L. aromatica, behind the DW that bisects the run of the tank. I just fed them lightly, and outside of 1 or 2, they refused to come out to eat.
They are not going high, to the surface, so I can't pin that this is a low O2 level/CO2 toxicity, but I'm stumped. Plants are really pearling now, so we're good there, but as I've had some issues with the cardinals, the last thing I want to do is stress and/or kill them.
Any thoughts as to what this behavior signifies, if anything?