What is up with my maxi?

[ReefAddict]

I'm hoping that one of you guys/gals can enlightment a little.

I've had this gold tear drop maxima for about 2+ years. I've tried everything to get it to set it's foot down. I've put it up high, middle, and bottom on a flat piece of live rock that was partially buried in the sand bed. No matter where I put it it jumps down to the sand. So I left it down on the sand.
It opens, closes, colors are good, it has grown since I got it.

Now here is what I find that is absolutely weird to me. She is always walking. Yes, walking! It will not stay put regardless of where I put it. The only way to keep it under direct lighting is to trap it between corals, even on the sand bed. Currently it has moved to the very front of the bow up against the glass from the middle of the sand bed.

It is being housed in a 155 gallon BF mixed reef under 3 X 250 watt 20K Helios MH & 4 X 24 watt PCs for the past year. Previously it was under 3 X 175 watt 10K XM & 2 X 140 watt VHO.
Par's
PH 8.6
SG 1.025
Temp. 78.6
Ammonia 0
Trites 0
Trates 0
Phos. I don't test since I don't have a Hanna Meter, but I can tell you I have no nuisance algae except inside the lip of my overflows.
Cal 445
Alk 9dKh
Mag 1350

Any ideas?

 

[WVUReefer]

?...sounds like its acting like a BTA..maybe it has to find a spot "it" prefers

 

[cumbeje]

I have several clams in my 730 gal reef tank. My oldest is over 5 years old and a foot long. The large one has never stayed in one place. I have found that the movement is usually caused by expelling water quickly when they are bothered. I have two blue ones and they have attached to rocks for years. I also think if they are placed in sand they will not attach to anything even if they are touching the glass bottom.