Ok so thanks for all the help/replies. I think it might actually be the large/extra large one
i measured around
Height: 25cm
Length: 40 some thing cm
Width: around 25 cm
On ebay the sizes are: Large: 36cm x 20.5cm x 25.5cm 8.75 Litres

Extra Large: 40.5cm x 23cm x 28.5cm 12.75 Litres
And also thanks for the tadpole food advice owler Its really going to help me when the frogspawn "hatches"?
Also should i use the blue on (i have been posting its sizes) or the black glass one that is really heavy?