I don't have diatoms in the tank but came across some articles which I thought might be interesting on the environment it prefers.
http://izt.ciens.ucv.ve/ecologia/Archivos/Tomas_references-II/articles/def/egge-jmarsys98.pdf
abstract:
"... results show diatom dominance when nutrients, including silicate were in excess. Diatoms, however, were not able to dominate when phosphate was deficient, although silicate and nitrate were in excess."
http://www.publish.csiro.au/FP/pdf/FP13247
"Generally, ocean acidification treatments of lowered pH with elevated CO2 stimulate diatom growth under low to moderate levels of light, but lead to growth inhibition when combined with excess light."
This was just a really quick look at if certain conditions favor diatoms. It seems that maybe keeping ph up may help. Not sure on the phosphate.
http://izt.ciens.ucv.ve/ecologia/Archivos/Tomas_references-II/articles/def/egge-jmarsys98.pdf
abstract:
"... results show diatom dominance when nutrients, including silicate were in excess. Diatoms, however, were not able to dominate when phosphate was deficient, although silicate and nitrate were in excess."
http://www.publish.csiro.au/FP/pdf/FP13247
"Generally, ocean acidification treatments of lowered pH with elevated CO2 stimulate diatom growth under low to moderate levels of light, but lead to growth inhibition when combined with excess light."
This was just a really quick look at if certain conditions favor diatoms. It seems that maybe keeping ph up may help. Not sure on the phosphate.