Here's an older view

Note the Hygro leaf holes, they are not present on the new leaves, nor the older lower leaves.

This is directly due to low CO2, the tank ran out on the client's tank.
You will note that it cause the leaves closest to the the meristem to suffer, while the rest of the plant was fine.

The expression of the holes took several days after the treatment of low CO2 occured.

Often there are developmental delays in nutrient expression treatments, generally a week or so.

If this where some other nutrients issue, such as K+ or NO3, the tips would be stunted or the lower leaves would have the patterning.

Such specifric and closely related nutrient deficiency issues are common in aquatic plants. Blackened Java fern occurs after slightly low chronic CO2 after about 2-4 weeks time. Mosty of the other plants did fine during this time. Adjusting the CO2 back up and waiting a couple of weeks restored nice new leaf growth with new leaves appearing and filling in about 4-8 weeks later.