Fish Tank Bugs In Gravel

How do these get in an aquarium?
I know that almost every aquarium has nematodes and/or water fleas in their tank. How do these get in there?
I know that the nematodes cause no harm and the water fleas can get eaten up most of the time but it is just killing me! Where would they come from if you only have fake plants and new gravel and a new, clean fish? It’s kinda creeping me out cuz I HATE bugs o_O
What is the purpose of the water fleas and nematodes? What do they do and why do they do it? I’ve seen a bunch of water fleas eating away a snail at a museum the other day and It kinda was freaking me out (Who wants a bunch of water bugs eating their pets?)…
Thanks!
I think they can migrate to new bits of water via eggs that blow around in normal dust. They naturally live in puddles and temporary ponds, when those dry up they leave tiny eggs behind that can be blown around in the wind. Some eventually end up in a new puddle, or even in your fish tank, hatch and if there is food they multiply.
What’s their purpose? They are an animal, they form part of the ecosystem and eat various micro-organisms and waste. If things like that didn’t exist, we would be over-run with dead snails…. So they are just part of a natural system.
To reduce theirs numbers keep the tank clean (gravel vacuuming) to remove their food source, and dont overfeed the fish. Less food = less scavengers.
Ian
Oscar means Buisness