What Optics?
 

What optics would you use if you had a DIY LED pendant that was mounted 10 to 12" above a tank? The tank is 30" deep as well.

Depending on the type and current LED s you are using.
for 3 watt or higher with at least 1 amp I would go with 90 degree lens as it gives it a nice spread.

The tank is going to be sps dominant. Are 90's going to be enough for a 30" deep tank?

Depending on the LEDS and the current they are driven at..as an example my tank is 31 deep and running DIYs 100 w led running at I believe 4 amps 2 feet from the water line with some 60 and 120 degree lenses no issues at all having SPS.

They're Cree's running at 1A and 1.5 amps between the royal blue and whites.

You should be good as long as you have enough of them over your tank ...either way I wouldn't go with less angle as it will give you as some say the disco effect.

Where would you say the cheapest place to buy optics are? I'd need almost 200 of them. Too bad I bought 150 of the 40 degree angles originally.

Send me the specs on you Leds as I will get a quote for you or send you directly to my supplier..

40 degree are ok but you need to mount those quite higher than the tank surface

I don't use any secondary optics on a 24" deep tank with the LEDs 8" off the water. Plenty of light for SPS all the way to the bottom. Tried 80 deg optics for the first 2 months, but didn't like the effect, too much top down light and not enough light from the sides. Corals look much better without the optics, and no "hot spots" or disco.