How do you know otocinclus(otto) catfish is doing well?

I have 2 otto's in a heavily planted 20 gal. with 5 neons. I just bought them a week ago, there wasn't much algae in the tank, they cleaned it all in a day or two. Now there is nothing for them to eat, i have been giving them pieces of bottle gourd and spinach (both microwaved in water). They seem to be sucking at the gourd but they are always sucking on the gl and ornaments as if they are super hungry. I don't know if they are hungry or they normally swim around very fast and nibbling rapidly? how do I know they aren't starving? I would appreciate any help.