Yeah providing the environment suited for them and a food source then they breed and multiply yes,there's literally thousands and thousands off species off pods,with majority being part off our mini cuc members and most find them beneficial to our tanks and alot off the fish we keep eat them,pods will eat left over food,detritus,algae on sand,rocks,glass etc.
And population off them in our tanks will grow and decline to suit how our tank is at that time ,so less food source or fish that actively go hunting the pods then population declines, then if no fish or food source goes up then population grows.
Pods even eat other pods,I've got a video off a largish ampripod chasing and catching /eating a smaller munnid isopod ( everything wants to eat everything in most off our tanks lol)
Not always but very often where you find the pods gives you a clue what they eat and if beneficial to tank or a pest, by that I mean is if find pods on glass they will be eating the film algae on glass.
If on rocks or sand then probably eating algae/detritus there,if find on a coral or near base off a coral then good chance its a coral pest ( but could be eating algae on or near coral or coral in a bad way or there's to many mouths in tank and not enough food source so have seen threads off people stating there pods are eating there " zoas " for example,if find a pod attached to a fish or fishes tongue/gills then a fish parasite etc etc.
But all in all,most reefers think off pods as beneficial to our tanks.
But like anything depends which kind you got and as there's thousands different kinds,sometimes can't be identified on a forum like this unless someone a marine biologist who specialises in them etc.
I couldn't watch your video as just got that spinning circle thing,it's often best to upload a video to YouTube then share link here and make NOT private,but I did see a little bit off video and looked quite large and could see with naked eye I think so my guess would be ampripods as generally larger than copepods and isopods in our tanks but in the ocean,there's isopods that reach 1 metre long ^_^
