Today, I notice one of the 1 month old platy fry had fin rot in its tail. Now he/she is the only one with fin rot so far. It's still eating and swimming find. I notice there were some fighting in the nursery tank too. What should I do? Another problem I have is that lately, my aqueon power filter has not been pumping out as much water in the aquarium. I rinse the catridge last week and I haven't change it since January. So should I look inside of it to make sure nothing is plugged up? Thanks.