Frogspawn and Tadpoles

[Kishimo]

How long does it take frogspawn to 'hatch'?  And why does it sometimes sink and sometimes float?  It was floating in our pond the other day so we gave some away but all the rest has sunk to the bottom of our pond.  Anyone know why?
Thanks.

[flaming]

Not sure about the floating but the blobs of spawn, but they may have been supported by tangled weed, which you aren't really aware of, whereas the other blobs were in water clear enough for it to drop down.  I think I am right in saying that blobs should not stay on the surface at the mercy of predators and pond surface frost. Also, as the developing tadpoles get bigger, like big commas, nourished by the spawn, one day there will be no spawn, only emergent little creatures!  Without you knowing there will be weeny tads swimming about down there within 3/4 weeks, I think. The tadpoles should gradually change shape, becoming more like froglets with little limbs and a stubbier tail;  when the tail is pretty well gone they metamorphose into proper tiny froglets, this happening over a further few weeks  - late June or July perhaps, depending on an individual's progress and success in getting food  -  weed when tadpoles but tiny water organisms when froglets.  They should all be "out" by August, although some advance more quickly.  (The spawn should have appeared by the end of March but who knows why the frogs were late in "delivering" the spawn? Perhaps you are in the north of UK?)  Unfortunately tadpoles are a tasty meal for pond fish and newts, if you have any.  Tiny froglets hiding, as they do, on or under foliage at the surface of the pond  (don't forget they breathe air at that stage) are the target of some birds.  There usually are only a few froglet survivors from the huge amount of spawn seen at the beginning of the cycle, with maybe a small frog or two at the end of it all, just in time to hibernate in mud over the winter.  It has been some years since I had a pond and I cannot say how the weather change has affected the cycle. The pond water must definitely be warmer now in the south of UK. 

[flaming]

P.S.  I realise you asked only about some spawn blobs sinking and others not but it was good to air my remembered knowledge about frogs.  Loss of pond habitat and food supply reduced by use of garden pesticides have caused huge problems for frogs during the last decade or so.  I am glad you have got a pond  with spawn in it.   The frogs need all the help they can get!