You can probably keep some low light corals with the 64w retro kit installed. Mushrooms and the like. You might be able to keep some thing with medium light requirement as long as they are up high in the tank...close to the lights. The problem is, with a deep tank, the light diffuses before it reaches the bottom. So, not much of your 64w is gonna get down there. My suggestion, and this may not be a viable alternative for you, would be to ditch the Eclipse and go with a canopy. In the canopy, either go with at least 4 32w PC
's or a 175w MH
fixture. I had the twin light Eclipse on a 10g and it proved to be inadequate.
In my 20 high, I have 4 scarlet hermits, 6 blue leg hermits, 5 astrea snails, 5 cerith snails, 5 nassarius snails, and 1 emerald crab. Tank stays fairly clean and no one is starving as far as I can tell.
I think the 200gph is not quite enough. It's best to have at least 10x tank size. You would need a minimum of 250gph and more would be better. As long as your calcium and alk
are right, and you've got enough light, your LR
should do well. If you do regular water changes, I think your trace elements will stay within accaeptable parameters.
If you can tell us more about the tank...such as what kind of corals you have...what kinds you want to get...pic of the tank would be great also...we can probably make better recommendations.