The Comet Balls were transformed by an Infected Mask, not directly by Kraata. Yes, Kraata are responsible for Infecting a mask, however in the Mata Nui Online Game, an Infected Mask was used rather then a Kraata (which had not been made in real life at the time the game was released). It is just my opinion, but I do feel saying the Comet Balls are tainted by an Infected Mask is or accurate then saying by Kraata.
It is actually the Kraata as we all know Makuta Teridax has/had Kraata hidden in his lair. He had used an Infected Mask on the Comet Balls...then it would effect Ahkmou too. Beside, how can you explain the slimy-looking green stuff on the Comet Balls? Knowledge can be anything or something you know about. (talk) 06:26, June 24, 2013 (UTC)
Okay, the reason I mentioned about it being an Infected Mask can be seen on my Profile page, showing 2 screen captures from the MNOG where this is from.
Looking on it, I guess it can be said that Kratta were used and the Infected Mask was just there as more of a symbol then the actual method of corrupting. As you pointed out, Makuta had several Kratta around his own lair.
Thank you for your thoughts in this matter: do appreciate you looking into this.