Why not use a submersible UV sterilizer such as this. While the unit is turned off place it over the area of the sand bed that has dino’s/cyano etc.. then cover with a opaque plastic box (maybe put a rock on top to keep in place), then turn on the UV. It shouldn‘t affect any living things (except maybe good bacteria in the sand bed) since it is covered. Probably wouldn’t need to be on to long (maybe someone has an idea on how long it would take to sterilize everything under the box. Probably would be smart to add some carbon to the filter since there could be release of toxins from dying organisms. This would be helpful for dino’s that dont leave the sand bed ( therefore aren't affected by an inline UV filter). Would’nt this be a rapid way to knock down a population of pests. Might be nice for spot treatment during an early infestation