Algae (and some other questions)

[acceberbex]

1) I have a guinea pig cage filled with water for my taddies (with land and bark for the froglets) and I've covered the sides with cardboard to stop them escaping through the bars. I've now put a plan of wood on the top to provide some more shade (it still lets a fair amount of light through though). The edges of the deep plastic tray are now covered in algae - it scrapes off but it would takes ages to clean it well.
Am I best to leave it (it makes the water look green as it's on all edges and the bottom), change the water gradually, or scrape some off (although it'll then float in the water and I wont be able to fish it out). I can't empty it and start again though (combo of froglets and taddies in amongst stones etc so can't catch them all)

2) I've had some froglets for about 3 weeks now but the rest are still tadpoles (most with backlegs) - will they get their front legs? They haven't changed for such a long time I'm wondering whether they are "stuck" in taddie stage. (It is hot here - about 30 degrees) so the water will be quite warm as well

3) One of my froglets had deformed legs - they were quite straight and he seemed to be "doing the splits" and couldn't swim well (he has now died - if he went on his back in the water he couldn't get back up and he must have gone over whilst I was out ) Is this normal for some?

4) I've been feeding them frozen bloodworms and frozen daphnia. How long should I leave the bloodworm in for - they don't always eat it straight away but it's usually gone by the next day. Since starting this I've noticed little things (bugs/insects) swimming in the water - they kind of remind me of sea monkeys but a lot smaller (but very fine). What are they? EDIT - Been to look today - they are dark now, no longer than 1cm with a blob body and a "bumpy" tail - like the side view of a spring but without being in a sprial if that makes sense

This is how much shade they have from the wooden plank
These are the water (second one has a taddie in there somewhere) - that's how green it looks but the water is reasonable (slightly yellow but similar to pond water colour)

Any advice/answers would be great - first year I've done this! *Sorry it's so long!*