Sudden Aggression in a Tomini Tang

[Jukas]

I've had a Tomini Tang and two false percula clowns in my tank for almost 2 years. The only even remotely recent addition is a CBB that was added about 7 months ago.

The tang and the clowns have always gotten along. When the CBB was introduced the tang chased him around for about 2 weeks but has since lost interest in harassing him.

In the last month or so the tang has decided that he must dominate the clowns. He keeps them confined to one side of the tank, and if he finds them too far out of their corner he chases them back into the corner and pins them down into the corner where the tank wall meets the sand.

I've tried upping the amount of feedings (I had typically been feeding once per day, 1 cube of mysis and pellets) up to double with no effect. The Tang gets seaweed once to twice a week and constantly grazes.

I'm not sure what's causing the sudden change in behaviour and I"m at a loss on how to resolve it. The tank is a 75g with another 30g sump and has been up and runnning for 3+ years. Nitrites are at 0, Ammonia at 0, Nitrates at 5-8.

[SDguy]

The addition of the CBB could have changed the dynamic, in addition to the tomini simply getting older/bigger.

Were the clowns always in the same spot, or did they change locations. Do they live in an anemone or coral?

[Jukas]

I too would have suspected adding the CBB, but he's been in the tank 7-8 months and this behavior has only been going on the last month. Wouldn't you expect to see the behavioral shift sooner if there was going to be one?

The clowns have always lived in the same general area, the right side of the tank. They used to host in a bunch of pulsing xena, but when I made a concentrated effort to clean up my water parameters it withered. They then moved to an under shelf area directly below the rock where the Xenia was on, and have seen been chased to the rear corner.

The clowns have never known anemone as I got them when the tank was "fresh" and didn't want to rush a BTA. My tank is established now but I just never got around to adding one. I would think in their stressed out state now they wouldn't be inclined to host in one should I add it. However the clowns are both actively still eating,they simply dart out and get food from the water column when the tang isn't looking.

Any suggestions on things to try and chill the tang out?

[SDguy]

You could try the old rearrangement of the decor trick. You could removed the tank for a while, and get the clowns an anemone, then reintroduce the tang.