A reader named Glenn recently wrote:
I have the icloud extra memory. I have a 16 gig ipad. I maxed out
almost a year back and added the icloud extra storage option. It
helped but no matter what I am constantly hitting the max on my ipad
even though I have tons left on my icloud storage.
Let’s address this. The photos and videos that you keep in iCloud Photo Library use your iCloud storage and your device storage. As long as you have enough space in iCloud and on your device, you can store as many photos and videos as you like. In this case, Glenn has plenty of space in iCloud but not enough space on his iPad. Here are a few things you can do to reduce the space photos and videos take up on your iPad.
iCloud Photo Library keeps all of your photos and videos in their original, high-resolution version on your iPad. You can save space on your device when you turn on Optimize Storage.
Settings > iCloud > Photos > Optimize Storage
Also check Setting > Photos & Camera > Keep Normal Photo
Make sure Keep Normal Photo is OFF.
Your iPad or iPhone has technology (HDR) that blends three separate picture exposures to create the best photo. You don’t need to keep the “normal” exposure too.
You can also save space when you shoot videos. Just above “Keep Normal Photo” is a setting to select the quality of video recordings. Choose 720pHD at 30fps (frames per second) to reduce the space videos take up on your iPad or iPhone.
Apple has more on photo storage at https://support.apple.com/en-us/HT204264
Learn Much More about using your iPad, iPhone or Mac