Diatoms is a algae problem that we all go threw. New tanks especially.  After seeing them grow and dealing with it i have finally found a couple of ways, alone or combined, that can help the issue(s). 

First thing is we have to look at what make Diatoms grow.  Light is one of them, you could not be giving your plants enough light to grow to use up all the extra nutrients in the water.  I did update my Lighting to a better LED system with that one on a 8 hour timer to insure that they get the 8 hours they need. This also depends on what you want to grow and it can very from not enough to too much light.  More than likely if they are getting a lot of light then this isn't the issue.  

Another thing diatoms need to live and thrive is silca/silicates, Nitrates and even phosphates.  The silicates can come from Fresh, untreated tap water, certain substrate, and so on.  Saltwater will have this more than other tho so keep this in mind.  The next thing is Nitrates, this is the ended produce from what your bacteria make and this is what give plants food as well, not just Diatoms.  Lastly and this is what did it for me was the phosphates.  This is what made my Diatoms grow and wouldn't go away.   

To treat the Diatom issue for me was i got a pad that removes phosphates from the water and strangely enough this also Clears the water! My water has never been clearer before this.  Once this is done i also bought two Japanese Algae Eating Shrimp and also a Algae eater fish.  Between these three things my tank is much cleaner with the normal Water changes and Tank wall scrubbing   

I hope this blog posts helps!