tz - as mentioned above, it very unlikely that Cutrine Plus would have any direct impact on your channel cats. But, with Cutrine - or any other algaecide or herbicide, killing too much algae or vegetation at one time could cause dissolved oxygen problems.
Actually, the label's suggestion to treat only a portion of the pond at a time (to ensure fish-safety) has no valid basis, since treating even 1/10th of a pond's alga infestation could send the DO-level below the lethal threshold if it is already tittering on that edge.
Warm water-temps, heavy buildup of algae biomass and/or insufficient aeration are just a few of the major culprits for such risky conditions.
I've never seen a risk-formula that takes into account all of the environmental factors to answer "How much of my pond can I safely treat at one time?" or "How soon can I make my second treatment?". So, I'd suggest that you err on the side of conservatism when treating algae with anything - especially during the hottest months of summer.
