Just my $0.02 worth...
I think if you stop those additives you'll stop killing off your diatom consumers and if you increase your circulation (a LOT!) then in a few weeks their populations will climb to the point where they will eliminate your Diatom bloom.
This isn't the quick fix, but it's the natural fix and will be a permanent cure.
The additives you are using a clumping the diatoms into an undigestible ball and your filter feeders are starving to death. The balls of algae are rotting and feeding the next bloom with their nutrients.
You can filter out the clumps if you clean your filter media every day but the bloom will probably return with the next water change.
Just a guess but I'd bet a frag that your Silicates read off the scale