Brown Spots All Over Plants

Hello,
I have a Fluval Edge 46L been up and running about 2 or 3 months with fish now post fishless cycling. However, I have noticed I have developed little brown spots all over my silk plants. See Picture. At first I thought it might be that sometimes the fish going to the loo and the fish waste dropping onto the wide flat leaves and the chemicals in it causing damage to the leaves but I have also heard that sometimes you can get brown algae but I don't know which this is or something different. As you can see, my plants are going browner week by week and it's making the tank look a lot less nice than it used to.
Every week I change 20-25% of the tank water whilst cleaning the gravel simultaneously and I de-chrloinate the new water and I use some Pure Balls to keep the water clear so I think I am maintaining ok.
What is going on in this case and what shall I do to fix the problem?
Thanks

Hard to tell from the picture but it just looks like you have diatoms developing. They're generally harmless, but they are ugly. Giving your decor a good scrub should help.

Looks like Diatoms. They are common in new setups. Unsightly, but harmless.
You could give them a wipe with a cloth to get them off the plants. They normally run thier course in a few weeks.

Yeah, I had these when I first set up my tank. I took out the plant and gently washed it. Then after a week or so diatoms never came back!