I've had frogspawn in my allotment bath pond for several weeks and noticed a friends similar but very clean pond has none as yet. I presume frogs must like something which resembles more natural sites as I always used to see spawn in flooded bits of fields and ditches. Some of them have hatched and I hope they'll survive the coming cold weather. Perhaps that's one of the reasons they lay so much spawn. With regards to the feeding, I felt there were so many in a small area that they would probably need supplementary feeding and a neighbouring plotholder said that she fed them cat biscuits. I know this sounds odd but once the little biscuits have got soggy they're surrounded by tadpoles nibbling away at the edges. Absolutely fascinating to watch. Didn't seem to do them any harm last year as a lot grew big and toddled off (probably miaowing as they went!)