I had 2 clutches with about 6 that had severe SLC. I changed over the vitamins to the Rapashy calcium plus and only feed them with spirulina and occasionally a few blood worms and I've been good ever since.
Didn't do anything else different, just the vitamins and I stopped rotating fish flakes in my tadpole feeding rotation. I just do straight up Spirulina and occasionally a blood worm or 2 when we give them to our fish. I also do water changes once a week. I read in a few posts that generally the first batch or 2 of eggs may be bad.
I follow what another member does on here, I saw him speak at Frog Day in NY and he has been in the hobby a lot longer then I have. I still do the same water changes once a week and haven't had any problems since my first 2 sets of eggs; which were laid super close together. I've had 2 batches come out fine and another one their way out of water which look just as good. I honestly believe it was the vitamins I was using.