For many years I had an abundance of frogs spawning in my garden ponds. This has all stopped within the last three years. there is no difference in the water (they are both wild, nature ponds) and have had no chemicals added. Other garden ponds in the area have their usual deposit of spawn. The only thing I can think of is that about ten years ago I installed a 'pestmagic', a plug-in device for chasing spiders etc. from the house. One pond is 6 feet fom the house and the other 15 feet. Could there be a connection between this gismo and the ponds? Naturally bred goldfish (which are still dark in colour) seem to thrive Ok.
Any suggestions would be much appreciated.
Newts and grass snakes can be responsible for disappearing spawn. I gave spawn to a friend in your situation and it had vanished by morning. Two grass snakes had a midnight feast.