Fish undereating and overeating.

Hello! I just got my fish (first time fish owner) yesterday from PetCo. Consists of two lyretail guppies, two fancy male guppies and two catfish or sterba's cory.

My problem is that my guppies are eating the algae tablet that are for my catfish, but my catfish aren't eating at all from what I've observed. I'm worried if I leave the tablet out too long, the guppies will overeat and that my catfish will be underfed.

Is there something I'm doing wrong? I read that the catfish would eat the fallen fish flakes and the tablet, but they've done none of that.. my guppies have been and they've been ignoring their feed.

I feed my catfish "Aqueon Algae Rounds Algae Eater Fish Food" and my guppies "TetraColor Tropical Crisps" - the saleslady recommended these. It's driving me insane because I wanted to be a good fish owner and this only day 2!

Any help would be appreciated, please and thank you.