Fish in my aquarium

Question
Hey there
I have had my pet fish for 5 months now, I believe its some type of mini looking catfish, but he sucks the algae off the sides of the walls, I got him as a present. Ive done regular water changes, fed him regularly, and have met up to all the requirements. This morning I woke up, and he was dead. He was laying at the bottom of the tank on his side, as I looked closer I saw tiny tiny white things swimming around the entire tank. They almost looked like sperm. However, I know sperm is microscopic. Its strange because they have never been in the tank before. Like I said, I had to look right up against the cage to see them. Theres probably like 60, they look like almost microscopic tadpoles, or sperm? They dont look like any type of worm, then again I could be worng? Please help. Last night my fish was fine, and when I wake up, he's dead with little white things swimming around the cage

Answer
One of two things happened here, I believe the cat fish you are talking about is an Otocinclus Catfish. These guys are good at cleaning up. Either your tank ran out of algae and he wasn't eating anything and starved...and the white things are some sort of parasite in your water that happened to be a coincidence.

Or you got a pregnant cat fish and it had it's babies, but the stress of giving birth killed it.

I think I might lean towards the babies side of it just because it would be really weird for the fish to die and then end up with random parasites in the water.

It is hard to tell without seeing them though. I hope this helps!