catfish help

Okay - so only two deaths. But still, two. And I'm really sad about my cory... so I want to make sure there's not something I can do to prevent any more... Yesterday I discovered a dead young male guppy - about an inch or so. Tested water and parameters fine - ph 7.6 (normal for here), ammonia...

Good morning all i have a tank approx 125 litres but just in the last week we have had 2 of our baby catfish in the tank are 3 adult catfish 9 gold headed minnow and 4 dwarf frogs the water is regularly cleaned as is the filter i have tested the water and the following are readings we always get...