Myfin,
Yes, I know I'll be having some difficulty with the heat. I've been keeping the place at about 65 degrees and at first, the temperature in the tank was rising above 80. I put a fan behind the fixture to help move the heat away from the tank and I also am leaving one half of the glass top flipped back to allow more evaporative cooling. This has allowed me to keep the temp between 77 and 80 degrees. I either will be buying a chiller or building an automatic water addition unit very soon. I shudder to think about the cooling bill this summer!
My fish are the sailfin tang, a small maroon clown (my Mom's fish - she fell in love with it - says I'm boarding it for her), a six-line wrasse and a couple of neon gobies (one of whom is living in the overflow because I can't catch him, yet. I don't know how he got there, but he seems well-nourished and doesn't appear to want back in the display tank. I think the six-line was being a bully). I also have some snails, a couple of blue legged hermit crabs, a couple of cleaner shrimp and two large featherduster worms. I'm sure there are many more things that I don't know about, yet. I have seen a crab a couple of times. I found it at night and it appeared to be eating algae. I'm hoping its an emerald crab. It is a pale jade green and has beady little orangish red eyes. I can spend hours at night with a flashlight and a magnifying glass; so many things to see and wonder about. It's kinda hard to get up to go to work the next day sometimes.
I wish you luck with the clam and the starfish. I've read that linkias are rather difficult to keep, but great detritivores. The mantles on some of the clams are absolutely gorgeous. I had a hitchhiker urchin in a past tank. It grew too large and began knocking things over. I eventually brought it to the LFS, but I don't think they sold it to anyone.
Oh, I reread my reply and realized that I didn't include the info about the lights. The MH are "10,000K Super Daylight double-ended HQI". I hope I can find replacements when I need them! I keep them on for eight hours. The actinics are on for twelve hours, with two hours before the MH and two after. I have the star polyps at about 1/3 of the way up from the sand. They are fully open most of the time, so I think they are liking things okay there. The xenia are just an inch or so above the sand in an area with good flow. I can't tell if they're happy there, yet. From what you say, I'm glad I didn't place things up higher in the tank! Thanks for your input.