Holes Appearing In Our Broadleaf Plants

[stackem evs]

All our broadleaf plants have small holes appearing in the leafs. I've only just noticed, but now that I have, they are in quite a lot of the leafs.

Suggestions what the problem is and recommendations to stop it please.

 

[Underwurlde]

Yellow spots on old leaves and yellowish margins on younger leaves. Pinholes appear which slowly enlarge = Potassium deficiency.

Possibility?

Andy