In my opinion, if you have diatoms, you must have a source of silicates somewhere in your system since diatoms require silica for the growth of their "shells".
If it were me, I'd try to find the source of the silica, and remove that source. If you don't you could quite possibly continue to see diatom outbreaks once the silicates build up over time. In other words, why only temporarily fix a problem, when you could fix it for good?
There are some other tangents that I'm not sure of, like the age of the system. If it's a new tank, I've heard outbreaks like yours. But if you have seen or continue to see outbreaks of diatoms, I feel sure that there is a constant source of silica in your system.
I could be WAYYY off in left field on this one, which is where I live it seems like, but that's just my two cents.