One of the things that we (as the all-grain brewer) need to keep in mind when using any false bottom system is that we, the brewer, create the most of the filter (via the grain bed.)
To do this we need to take care of the grain bed during set up, milling, vorlaufing, and sparging. Here are a few tips to avoid excess grain getting through the false bottom.
You will want to check to see if the silicone false bottom gasket (black) is fitted up properly to the false bottom. Make sure it does not slip off when you put the false bottom into the mash tun. You can spray a little sanitizer around the edges of the gasket to help it slide in easier if needed.
The false bottom and our silicone gasket that seals up to the side walls is just a tool to be used to keep that filter above the drain port of the kettle or mash tun. Know that ANY grain that is dumped on top of the false bottom can get through if it's smaller than the holes in the false bottom.
Be sure your mill is correctly set to prevent a disproportional grist ratio from powder to coarse crush. Since grain is grown and thus varies in size, you may need to adjust your mill's gap settings per grain type to get the most out of each variety of grain. If you are using a common friction-style knurled mill, this may be difficult to consistently achieve. We recommend our Ss Grain Mill for quick and easy adjustments.
If the mash was made with too fine of a grist, it can still clear up, but you should take a close look at your mill setting. It also could be that you just didn't have much / enough grain in your grist. A really thin layer of grain will never set very well and will pass more grain through under the false bottom. That's simply because there's not enough thickness to create a good filter. We recommend a ratio of around 1lb of grain per 1.25 quarts of water.
If a lot of the particles you are seeing are really small, but larger than a powder - it could imply the grain bed didn't get set properly. Most brewers have seen clear wort after just a few quarts of vorlaufing. But depending on your mill settings - could be more or less than that. It can help to slowly crank up the flow during vorlaufing to help to set the grain bed. Creating a higher flow rate suction under the false bottom during vorlaufing will help get small bits of grain out of there.
After vorlaufing (and mash recirculation if you aren't doing single infusion,) you can dial back the flow for the Sparge process as needed for your system. One key point is to drain the liquid down to have between 1/2" to 1" of liquid above the grain bed. The bed will compress, as you start pulling the fluid off. You should be able to see the liquid level, once you hit the 1/2"-1" you can pour the wort back over the top of the grain bed until it flows clear. If you have too much liquid in the Tun, the bed will not compress properly. This compression or "set" grain bed proves both sparge flow rate and natural filtration are correct.