Raising ACF tadpoles

[Gemma]

I have a few questions, if anyone can help:

1) I've noticed a few of my larger tadpoles coming up to the surface of the water for air a few times. They don't do this often, but I've noticed it happening 3 or 4 times over the last few days. They seem healthy, I'm doing regular water changes and I have an air pump in there on a low setting. I know that eventually they will be breathing at the surface, but they've only just developed their back legs so I'm not sure if it's normal for them to be doing this already. Does anybody know?

2) Once some of them have morphed into frogs and I have separated them from their tadpole siblings, is this when I should introduce a filter to the tank, rather than just an airstone? The reason I'm asking is because I only have one air pump, so I'm wondering if I'll have to buy a new one for the newly morphed froglets, or if I can just use a filter with an air pump attachment? They don't even have arms yet, but I just want to be prepared.

3) The videos and photos of ACF tadpoles that I've seen online always have a thin coating of food (and tadpole waste) on the bottom of the tank. My tank never looks like this. I was feeding them twice a day up until they developed legs a few days ago. Now I'm feeding them 3 times per day, but there's never food resting on the bottom. Should there be? I haven't read anywhere that the food should coat the bottom, but all the pictures/videos that I've seen are like that. 70% of the tadpoles are large and growing very quickly, but the other 30% are a lot smaller than the larger ones were at their age. They are growing, but nowhere near as quickly as the larger ones. I'm not sure if this is just a case of individual tadpoles developing at different rates, or if the larger ones are filtering out all the food so the smaller ones aren't eating enough?

Thanks.

[Gemma]

One of the tadpoles has arms now :) The rest of the largest ones are getting arm buds!