I just got 2 oscars (from a pet store) in a twenty gallon aquarium and i had 2 sucker fish (from walmart). Both of my sucker fish died. i think its just because of walmart. But anyways I am looking at my oscars and I see that there is little tiny white dots all over them not just by there gills but just all over. I went to walmart and got some tablets that kills parasites, I changed out 50 persent of the water, then did the treatment again and they're still not gone. What can i do? or am I doing something wrong?