Who Gives A Fish Forums

I was thinking of doing a video to show you all, but to be honest, the water's too murky, so it's not worth the effort. I picked up some big clumps of blanket weed from the LFS pond plant section and I've got it in a tiny tank in the garden. There's loads of stuff running around in the water - all shapes and sizes, and some of them are moving pretty fast.

I know I don't have any pictures, so I'm just looking for some educated guesses here. The smallest ones remind me of daphnia in the way they move, but these little things are dark black and maybe a bit smaller than daphnia. I found some things hiding under the blanket weed that look like underwater beetles - they're grey/silver and about 5mm big. They move really fast, darting around, and I think they might have 5 little legs on each side, but I couldn't get a good look.

The small wrigglers at the bottom are pale and transparent, so I'm guessing they're some kind of larvae. And then there was this one creature that looked like it was training for the Oxford/Cambridge boat race - it was the biggest one I saw.

So, I've got a few questions:

1. I'm thinking of raising my own live food for corydoras and small tetras - is it worth the hassle? Is it too risky for the fish?
2. More importantly, are any of the things I've described likely to be a hazard to fish - not just in terms of pathogens, but also in terms of physically being in a fish tank?
3. Based on my descriptions, can anyone take a guess at what some of these things might be? I'm in the UK, by the way.

I've been doing some digging online and looking at pictures, trying to narrow down what these little critters might be. I think some possibilities could be water boatmen, water slaters, or maybe even mayfly larvae - those last ones seem pretty likely given the description of the pale, transparent wrigglers at the bottom. There's also the water hoglouse, which seems like a good fit for the grey/silver, fast-moving things hiding under the blanket weed.

And then there's the tiny black slug-like thing on the sides of the glass - that thing moves ridiculously fast, at least three times as quick as a snail. I'm not sure what that one is, but it looks a bit like a leech to me.