What would cause an RBTA to wander at night?

[Canarygirl]

My RBTA likes to go walkabout after the halide turns off and there's just the actinics on. He has started doing this 5 nights out of 7. It's been going on for ~ 1 month, and before that I had him for 3 months and he never moved at all. Lately when he goes walking, he usually wanders towards the Koralia powerhead and I frequently have to peel him off the tank wall to get him away from it. I don't like worrying about him this way...

do you have any ideas on why this could be happening?

The tank is 5 months old, the light is 1 250-watt 12K Reeflux on for 6 hours and 4 PC actinics (28 watts each), on for 12 hours.

It's a 30 gallon cube with an 800 gph Korallia plus the return from the sump. The cube is on a shared system, 145 gallons net water volume.

 

[ReefNeck]

It's just something they do. May not like flow or looking for light or just a comfortable spot.

Nobody knows for sure and there is no way to ensure they won't move.

 

[Toddrtrex]

I don't think it is just something they do -- they will move when something is bothering it.

Mine hasn't moved in a couple of years (( even stayed on the same rock after I re-did the tank ))

Besides the lights going off, does any thing else happen at night? -- skimmer shutting off, powerhead coming on or off?

Wondering if maybe there is a big temp change, pH swing, or a lesser amount of oxygen in the water at night. Perhaps do some water tests during the day, and then at night to see if something is off.

 

[55semireef]

They will stay put when they are "happy." You have enough light but your flow may be too high in some areas or its just that your 5 month old tank is bothering your RBTA with its water chemistry. I am betting it has something to do with pH. Newer, unestablished tanks are known for going through pH swings and this happens at night. Test your pH right before the lights go out and 10 minutes after they go out and compare the two.