Diatom on sand bed

[lovefishys]

We have a 75 gallon SW. It has been up and running for about 3 months. We have a 20 gallon sump, protein skimmer rated up to 300 gallons, levels are good, ammonia 0, nitrate 0, nitrite 0 and ph 8.3. We only use RO/DI water. With weekly 15% water changes and cleaning of the sand. But we are still having the diatom growth on the sand and acrylic. I am not sure what we are doing wrong. Any help would be great!
Right now we have a fuzzy dwarf lion fish, hermit crabs and 2 snails. We are target feeding the lion fish so we are not over feeding. I believe that's everything.
Thank you!

 

[Hondatek]

If it's just diatoms it's just a waiting game until all the silicates are used by it.

 

[crister13]

Ya, every tank gets them.