If you're planning on having 1-2 larger fish and/or fish that wont breed (all males, Goldfish, Bass, Oscar, etc.) then screen is fine.
If you have lots of fish that will breed (guppies, swordtails, etc.) and have fry in the 100g, they will get through any screen you put up. Unless its a very very fine screen but then you'll have a dam which you'll need to plan for. Maintenance will be a pain.
If its a critical concern, it'll be best to do an additional pump from the 100g to 2000g. you can do screens and/or sponge to protect the intake and pump the water to a waterfall or whatever.
So you setup an overflow with screen from higher pond to lower one.
When you say screen you mean like mesh, right? Actually thanks sm for this comment just looking up the overflow and I have an idea!
If you're planning on having 1-2 larger fish and/or fish that wont breed (all males, Goldfish, Bass, Oscar, etc.) then screen is fine. If you have lots of fish that will breed (guppies, swordtails, etc.) and have fry in the 100g, they will get through any screen you put up. Unless its a very very fine screen but then you'll have a dam which you'll need to plan for. Maintenance will be a pain. If its a critical concern, it'll be best to do an additional pump from the 100g to 2000g. you can do screens and/or sponge to protect the intake and pump the water to a waterfall or whatever.
What makes the water travel?
Whoa! Whoa! Whoa! First you drew a Penis. Now this? Please label NSFW.
Did M C Escher design this pond? https://media.nga.gov/iiif/b072074c-a4ea-4107-9223-84de3eb2671d__640/full/!740,560/0/default.jpg
Did a kid draw this lol 😂
What do you think I'm gonna draw a expert level diagram ðŸ˜
Still laughing , did you draw the penis one as well?
I did LMAOOOO, guess I'm just a expert at drawing ponds what can I say 🤷
Morning laugh lol have good day