what count of plastic cavas to use?

[Rumpy Pumpy]

I'd have thought the smaller the holes the better as it'd give more surface area for algae to attach to?

[SantaMonica]

That's not the issue. The issue is that as it grows, algae shades the screen, no matter how much surface area there is. So the goal is to grow as much as possible before the roots die. Once the roots are shaded you only have a few days before they let go.

[dirk_brijs]

so have said that would a 14 count work?

[SantaMonica]

Probably