Causes of diatoms
Virtually all new aquariums will go through a diatom bloom, which is nothing to worry about. Once they’ve reduced the excess nutrients they thrive on – particularly silicates – they will die back and other algae will move in unless limited by plant growth. In more mature aquariums, the cause of diatom blooms may be excessive nitrate and other nutrients, a lack of light – which diatoms don’t really require but which will stunt other competing plant growth – or insufficient oxygen.
Treatment
In a new tank, just wait until the bloom passes. In an older tank, do a clean-up and several large water changes to reduce the nutrient load. You may need to treat your tap water if the problem is persistent. As with all algae solutions, heavy plant growth will out-compete diatoms – you’ll need to provide sufficient lighting and the correct micronutrients for plants. Some fish and snails will browse on diatoms, but only a full environmental clean-up will suppress them if they occur in mature tanks.
I suggest a big water change of 40%-50% of your tank, second would be to add some more anubias plants, or java ferns to the tank, and try to clean the gravel with a gravel vac. For dosing the flourish comprehensive, I would dose it on Wednesdays, and Saturdays because it gives the plants a couple of days in between doses to soak up the nutrients.