55 tall diy led help

my 55 is only 30 long, 24 high and 18 deep. i have the fixture about 12 inches from the water and it punches through the water. my sps are looking happy and growing so the light must be working lol....for your 36 inch, it might not cover all the edges of the tank and maybe a second fixture will fix that for you. if you do get two fixtures, they will be more than enough light and you'll have to turn them down a bit on the brightness or mount them higher. I know 3 fixtures are enough to cover a 125 gallon tank with sps.

 

I saw these at a lfs and one was enough for his 40B frag tanks 36X18. For the price, as long as you don't want/need any extras, it is the way to go.