Holes in leaves help

[Buckfins]

Hi all....I have a nicely planted 55g. I feed it flourish excel on a regular basis. They plants are growing nicely, but I have noticed holes on several leaves. What is causing this? Is there a lack of some fert that I am not applying? for your help.

 

[Bert2oo1]

Hi all....I have a nicely planted 55g. I feed it flourish excel on a regular basis. They plants are growing nicely, but I have noticed holes on several leaves. What is causing this? Is there a lack of some fert that I am not applying? for your help.

It could be a fish or a snail? Or this may help you out. It's very basic but a good start.