New White Sheet Growth

Hi,
I just set up a new 10 gallon tank the that been up and running about 4 weeks.
 
I have 2 male and 2 female guppies which are doing ok.
 
The issue I have is that there is this white growth, and I am not sure what it is, or what to do about it.
 
Any help would be appreciated!
 
 

I get something similar looking on rare occasions in a couple of my tanks. I live on an acreage and have well water, which comes directly from an underground aquifer which runs 350' deep through limestone. Thus, my water is very hard. We filter it, which removes much of the calcium, but when I become lax on changing the filters, I seem to get the filmy growth after water changes. I attribute it to excess calcium in the water. My more knowledgeable friends assure me it isn't a fungal growth, and not dangerous to the fish; just unsightly. I can't say that yours is the same, but it certainly looks like it.