Adding bacteria to a low nutrient tank may not help as much as you think.
Diatoms grow with Silicates, so I assume you may be talking about Dinos or cyano.
Dinos or cyano can grow due to low nutrient levels. Typically bacteria in a bottle grow using nutrients. Therefore if you have low nutrients, my experience has been bacteria in a bottle when used alone, will likely not increase in population to overtake your dino or cyano problem.
What has worked for me:
1. Increase my nutrients by dosing nitrate and phosphate. (measure your levels of NO3 and PO4 after adding into tank---i.e. I add NO3 of 10ppm and PO4 of 0.1)
2. Add the bacteria in the bottle to the tank
3. Add enough of a carbon source to feed the bacteria in the bottle.
3. Take the collection cup off the skimmer so that you don't skim away the bacteria in the bottle species. You still want to aerate the tank and keep the pH up.
4. Black out your display tank (also sump/refugium if you have light in them) for at least 2 days
5. after 2 days, you should have a much cleaner looking tank-- remeasure your NO3 and PO4 to make sure it is not zeroed out.
My belief is that I have grown enough bacteria in the bottle to outcompete the dinos/cyano. As long as I don't bottom out my nutrients- they shouldn't come back.
Have you also looked into seeding your tank with copepods such as Ecopods from Algaebarn?
