Hi Cockatoo,
I am not sure where you are from, suggest you get your details on the board.
Grunter is most likely the most difficult fish to target on fly, but when you get him extremely rewarding.
I have fly fished extensively for Grunter in Durban Harbour and in the Umgeni River Estuary with a fair amount of success, my best Grunter was around 5Kg, and on a 4wt rod.
This is what worked for me - Use it don't use it.
Grunters like to feed mostly on small crustaceans, and they do this by forcing a jet of water into the sand which blows out the crustaceans which they can sense and from there they eat them. You now need to try and get your fly into this jet zone and this is mostly done by sight casting, which is the only truly succesfull way I have managed to get all my Grunter with the exception of 1 fish (my biggest) which I got stripping a large pink clouser on the top, I am still trying to figure that one out. But there are only general guide lines to fishing, and the fish do what they want. Still I only call a method once it has produced several fish.
I have found that the Grunter like to come onto the sand banks and start feeding as the tide starts coming in, and this is even more so the case when the incoming tide is in the late afternoon.
You need to go light so a 4wt - 6wt rod is what is needed, at Umgeni Mouth I use a 4wt as the Grunter are generally smaller and in Durban Harbour I use a 6wt as the Grunter are generall larger.
Sinking Line DI3 or 4, I use DI3 which is perfect as you are generally fishing for them in 500mm or less of water. The reason for the sinking line is to get it on the bottom so you do not line him or spook him, let it sink out of sight. I like using a dark brown line.
Leader 4lb to 6lb flouro (the lighter the better the chance of a hook up) and 2.5 - 3m long. It must be long as when you sight cast for them your fly must pass him, but not your main line.
Fly: I tie a small modified Crazy Charlie with a slightly longer tail than usual using white feather hurls and white rabbits hair dubbing on the shank with copper wire wrapped under the rabbits hairwith very small black bead chain eyes. It must be a light gauge size 10 trout hook. The copper wire wrapped creates an electro field and I then also magnetise the hook and keep them on a magnet right up until I need them, the electric feild is important. I also rub the fly in the sand before I use it to dirty it a little and take the brightness of the white.
You will see them tailing on the banks (this is when they areblowing the water jets into the sand) right into ankle deep water, you then watch and see what direction he is moving and cast your fly, but not the line past him and let the line sink and settle. Then you time him and slowly slowly twitch you fly into his path, and hopefully it blows up with all the crustaceans and he senses the magnetic field and takes your fly.
Hope this helps. :fishn
See the pic of my one around 5Kg attached that I got in Durban Harbour, I got him right in the shallow water by Cafe Fish standing in the parking area by my car at night whilst going for Sea Pike on a Size 1 Pink Clouser stropped fast on the surface. Figure that. Prooves my theory that the best way to catch fish is to get your line in the water.