If your opponent is going all hydras, the best way to counter them is with the method I said above. Upgraded zealots will totally own hydras if you send enough of them. Dragoons own hydras also. If he hits your 3 bases at once, then what do you think arbiters are for? You can transport guys from any spot, to any spot in a matter of seconds using arbiter's recall, so just keep an arbiter at each base. Also, keep an arbiter near his base and if he sends all his guys, go into his main base and warp 12 dragoons or so into it and kill off his main base, that will usually be enough to get him to recall. All this said and done, the fact is...like I said above, there is no easy way to beat a good zerg as toss. You need to be creative. If you think you can beat a zerg who makes all hydras by just making zealots and dragoons, or any other type of units, you're nuts. Hydras are too cheap and can be made too fast... so you need to use the tools that are given to you, such as Reavers, Archons & Arbiters. Also, another good weapon is temp's storm... and dark archons as well. Start using arbiters though. I know they are hard to get, but work up to them and once you get them, use recall like mad.