Yeah, not so sure with the Colossus. I haven't heard much, but it always fires indirect and is crippled by a massive minimum range of 36". By contrast, the Griffons have only a 12" minimum range and have the AWESOME "Accurate Bombardment" rule. You may want to consider a switch to Griffons in the future so you can cripple Tyranid armies.
That being said, I think with all the Hydras you won't have too much trouble with AV12 armies.