Hi i'm ogl and I want to share what in my opinion is the best way to get a LOT of gems.
First you need to get an ocean claw machine . These can be hard to obtain, not a lot of people have them and the people that do don't want to trade them. I have one and my den is always open if you want one.
next follow the instructions on the Tips for getting rarer page. It explains how to continuously get plushies from a claw machine.
Once you have an ocean claw machine and follow the instructions, recycle all of the plushies you got. Each one recycles for 150 gems because they were buyable in the summer carniva rather then the usual 15 gems on on most plushies.
you will get lots of gems depending on how long you afked getting the plushies, if you have membership and have all 1000 den inventory slots avalible, you will get 150,000 gems per session.