Very bad gnat problem please help :(?

Okay i have a red eyed tree frog... and a year ago i saw hundreds of these small gnat like things everywhere in the tank! They get in my drinks...food there everywhere. ANNOYING and i have eating prob 100000 of them :'( I cleaned the whole thing out all the cocanut dirt stuff and got new stuff.... new fake plants everyting... they came back... but this time triple the amount of them!!!! theres thousands!!!! in the tank. does my frog eat them? do they hurt my frog? and HOW do i get rid of these things? PLEASE HELP