I assume that 55 gal is approximately 48 x 21 x 12.5
I am struggling with mine, right now. What light(s) are you using?
I have two of the Coralife fixtures, one on each of my 29g tanks - I have never had a problem with mine in the 2 years I've had them, but there are threads where people have had trouble. I like mine.
However, I bought this for a low light/low tech 55 that has since been torn down - now I use the light on my 125. You can see more of it & how it looks in my 125 tank journal under my signature. I LOVE this light! Inexpensive, and the bulbs are very, very inexpensive. If you check my posts, I have plenty with pics of the tank (haven't gotten far with the journal yet) and you can see how the tank looks lit...