Weak egg shells a soft eggs

[2peasinaprod]

Hi,
Any advice on what to do for my hen. She's been laying very weak shelled eggs for about 3 months now and some days they are just complete soft with no shell at all. She's 3 years old and seems perfectly healthy in every other way. There is normal grit and a separate container with oyster shell always available.
Thanks you

 

[rosemarythyme]

What type of feed do you use? Any treats or extras and if so what kind? Have you tried directly supplementing her with calcium and if so what were the results?