I used the PAR meter to match the PAR of my new 250watt Phoenix Metal Halide, which turned out to be about 5 inches higher than the original hood position on the clam tank about a week ago. The PAR value under the bulb at two inches was originally 95. A week and a half have gone by and I moved the hood down 5 inches which now has a PAR of 112 at two inches of depth - same position. How much farther do you think that I should plan on moving the hood down in the next several weeks? The two inch depth is approximatly where the first coral is under the waters surface. The outside edges of the tank drop off to a PAR of around 65 at a two inch depth originally and are now at around 78.
Thanks Joe for the link. After doing some reading it is still difficult to get peoples reports of what actual PAR values that they are using at any particular depth or placement in there tanks. I am just looking for a general number to start at and it is difficult to find. I have moved from a PAR of 90's initially to 112 at two inches of depth directly under the halide. I think that I will make another move down of the halide (5 or 6 inches) in a couple of weeks and shoot for a PAR of around 175 at two inches depth several weeks later. I will update this post and let everyone know how it goes.
