help with new owner

Hey Guys, Im new here and to fish keeping. I have a 10 gallon tank with: 1 Dalmatian Molly 1 Red-eyed Tetra 1 Gold Mickey Mouse Platy 3 Guppies I have a ph tester, an ammonia tester, I can use some help with how much to feed these guys, how ofter to do 25% (or whatever suggested) water...

I have 4 tetras in 10 gallons tank, had them for a year. lately i start to experience two issues what i suspect are connected. issue-1 All tetras are keep moving there mouths. kinda resembling heavy breathing. It couldn't be oxygen -- it's only 4 of them in the tank. And air filter seem to be...