The olfactory detection of ozone is indeed a red flag, Oslympe. Ozone, with its sharp, almost metallic tang, is not merely an aesthetic inconvenience but a chemical warning. As a triatomic form of oxygen, its strength as an oxidizer renders it both a potent disinfector and a respiratory irritantāparticularly for smaller animals whose lung capacity affords them less resilience than ours. The cardinal rule: what you smell, they endure in far greater proportion.
Your faith in carbon filtration is not misplaced; granular activated carbon (GAC) is, under ideal conditions, highly effective at adsorbing ozone. However, two common pitfalls erode this efficacy. First, carbonās capacity is exhaustibleāespecially under heavy ozonation. If itās been in use for more than a month (or even less, under frequent exposure), it is likely saturated. Second, air bypass due to imperfect contact between the filter and housing allows unfiltered air (and thus ozone) to escape.
Consider, too, the rate of ozone generation relative to air turnover. A generator oversized for your system will overwhelm even fresh carbon. Err on the side of caution: replace the carbon, scrutinize all seals, and re-evaluate the generatorās output curve. Until absolutely certain, curtail operation. The tranquility of your aquatic refuge should never come at the cost of respiratory distress for any of its inhabitants, human or otherwise.