Just got new fish & there eating off the plant's and tank and heater.? why?

i have 2 kisser fish and 2 tiger sword tailed fish. i got the 10 gallon tank yesterday and set everything up. heater, filter. thermometer, air pump. i have about 6 fake plant's in the tank. i also put the conditioner in the water and waited 24 hours before i put the fish in. but my 2 kisser fish i been watching and see them like suck on the plants and the heater. i tried putting a little bit of food in case they were hungry but the 2 tiger fish ate it and the kisser fish didn't seem interested.! why is this.? & what do i do. thanks.