Watts per gallon or depth of tank rule?

[jimi thing]

Now I know a lot of people still go with WPG when it comes to lighting reef tank but doesn't it really boil bown to how deep the tank is?
The reason I ask this question is because I know some people with 12g nanocube tanks (14.8"H) with a 70 watt MH over the top and they are keeping some SPS and some even have clams. 12 gallons with 70w=5.83 WPG. I have a 70g long, low tank and I'm wondering if it would be the WPG rule or depth rule on my tank. I have 6X39W t-5's over the tank now but got a really good deal on 2 70W HQI's. After seeing how awesome the colors were and the shimmer I knew that I wanted MH not just T-5's. I hooked them up and set them up about 3" off the water line. My tank is only 14.5"H and the distance from the light to the sand is 16". I was planning on getting a third for the middle of the tank.

So my question is will 3X70W HQI's and 2 39W T-5's over a 14.5"H tank be enough to get a some SPS's and maybe a clam?

The T-5's only just look so much brighter than the MH w/2 T-5 act

Here's the HQI and 2 39w t-5 act.

http://i57.photobucket.com/albums/g230/glenjerome/salt407.jpg

Now here's just the 6X39W T-5's

http://i57.photobucket.com/albums/g230/glenjerome/salt390.jpg

The only other thing that I could do is combine all the lights.
Any advice would be great!

Thanks!:)

[RONCGIZMO]

I think you're 100% right about the depth thing..
I also think your tank would be more then fine with the T5's you all ready have. from what I understand you can have clams with the T5
without issue..If you want to kick it up a notch upgrade your ballast
to an ice cap and overdrive the suckers :) from what I'm reading if I change out my 75w T12's for 24w T5's I'll get 40w with my ice cap.

[siwelk]

T5s FTMFW

[pjf]

I would think that the live rock in your tank has much to do with light penetration at depth. After all, a home aquarium is still rather shallow and the glass sides of your tank act as reflectors. "Shading and reflecting light out off objects in the tank are the significant factors in light being lower at depth than near the surface." - Wright Huntley, San Francisco Bay Killifish Association

Without a light meter, the next best thing is a guide to lighting and depth recommended by The Grim Reefer: http://www.advancedaquarist.com/issues/august2003/feature.htm. You can also check out page 448 in The Reef Aquarium, volume 3.

[jimi thing]

Thanks guys!