Ruth

I usually shoot for a KH of 8dkh or approx. 2.9 meg/L alk.

I have 3X 400W MH - 4X65W PC over my standard 230g tank. HTH

That is what I am thinking as well.

I would just vacume the sandbed a bit when you do a water change to stir things up a little. Like I said it doesn't usually spread on the sandbed - you might need a bit more flow in your tank. Coraline doesn't usually like really intense light although it will grow. I notice that it grows the best under VHO lights (at least in my tanks). Just make sure it isn't cyano - if it is vacume as much as you can out of there. Is it hard and crusty? - or slimey?

Coraline algae is a good thing (usually) but does not usually grow on a sandbed unless it is a faux sandbed glued down. The reason is that there are usually too many critters in there moving and shifting the sand. Make sure it really is coraline and not pretty purple cyano algea which is not a good thing.

FWIW I have a 10g tank set up and have a 20" coralife PC unit set up on it currently. I am going to change this to a 150W MH pendant that I have because I would like to keep a clam in there. It will be quite far off the tank surface to avoid heat issues.

The other very important part of the calcium/alk. equation is magnesium and you should be testing for that as well. If it is out of whack you are never going to get a good balance between your calcium and alk. Your magnesium should be about 1350-1400 ideally. If it was me I would do about 3 50% water changes over a course of 3 weeks (1 a week) and test every time both your newly mixed up salt water and your tank after you have done the water change. IME the Salifert test kits are much more accurate and easier to read and when it comes time to replace you kits you may want to consider that. Your test kits are getting old as they are usually good for about a year unless otherwise specified. HTH