sounds like from your description that they are copepods...we had those in my shellfish tanks at work (well salt water variety of course...) but yours sound like fw copepods. They eat algae as well. If they are only copepods they are essentially harmless since they are not competing for food in your tank..The copepods will look like tiny flailing white creatures moving awkwardly around your tank. To get rid of them drain your whole tank and clean the tank walls rocks thoroughly with hot water, that will normally get rid of most of them....or you can just keeping their population down by sucking them up with a siphon when you do your weekly water changes
they sound too small to be lice from my experience lice are huge (well in comparison lol)
or they could be the free swimming ich, if your fish gets white spots all over it then you need to either salt water bath or treat your fish with medicine and clean the whole tank!
but for now it sounds like copepod
I forgot to mention when you rinse your tank I would add some salt in there too, since they are a fw bug. The salt + hot water should kill them.