I have set up a blaze farm on several single player and Multiplayer worlds. I typically use soul shards and farm them, but that only pertains to getting them to spawn. If you have spawner that is successfully loading blazes in your overworld then the water cage will work. If you are looking to only collect rods and not exp you do not need a player entity (yourself/turtle) to kill them water will work fine. Set your room up where all the water filters to either a central collection point or to one side. If you want to grind exp off it you will need to kill them yourself or set up some melee turtles. The problems you may be experiencing could be due to a few things. One blazes don't always drop a rod when they die. So using a vanilla spawner instead of a tier 5 spawner/soulshard, will net you fewer blazes at a time. Less blazes=less chance of rod drop. Number Two, you said you are using a hopper? I assume you mean the 5 iron,chest, and stone gear recipe to collect the rods? I could be wrong but they seem to need to be fed forcibly either by pipe,tube, or gravity etc, and won't simply "suck up" any dropped rods. Try using a transposer into a tube or pipe system instead. Note: they tend to need a pulsing red stone signal to function in ultimate. You can do this a few ways but the simplest is a redstone tube, cobblestone structure pipe, and an anarchic gate. Set the gate to if no redstone signal, then red stone signal. This provides an infiinite redstone pulse, Note: did not work when set to energy pulser and will sometimes stick on reload. Clears up if you either look at the gate gui or simply toggle a red stone signal on and off, such as a lever, or for more complicated master switches I use wireless redstone to toggle multiple gates to ensure all affected redstone pipes start working once I relog or come back from a dimension etc.