crocea

I think it's safe to say you have an established tank

 

does that make the crocea safe?

 

i think you can try it, just watch it if it starts to go down hill take it back or give it to someone else, and put it up high in the tank

 

ok, what are the downhill signs?? and what could i add to maybe give me some extra success...

 

not opening, im not a clam expert so i would get someone else's input. extra success, new t5 or metal halide lighting(i know thats not what you wanted).

 

Some downhill signs are if the clam isn't opening or if it is too open. If it is too open, that means that it is not receiving enough light and is "stretching" to try to get every zoo cell exposed to the light. Generally, if the clam doesn't look healthy it isn't doing well. Look for proper coloration too. Remember, clams take a while to die, so it may seem fine for a while but then end up dead. After a few months, look for new growth, it will appear just under the mantle at the top of the clam as a very white part of the shell. Mine has grown about a quarter in. since I have had it.
One tip, get some filter feeder food and use that to help supplement its nutrition.