That's weird as you usually see filter regulations that require separation tanks, not exact filter types. The funny part is, you still need to tear down a DE filter regularly (like once per year) and do a deep clean of the cartridges or grids. You can backwash the filter prior to opening it, but that only gets rid of maybe 50% of the DE that you need to clean off. The rest comes off on your lawn or "back 40" when you take apart the grids/cartridges for cleaning.
So in the end, the regulation is kind of useless since you will still be discharging DE into the environment...unless you plan on being a "good citizen" and figure out a way to capture all the DE crud you wash off.
