When the older leaves are affected but new growth is not it is likely a mobil nutrient deficiency. Plants can remove some nutrients from old growth to support new growth. Most nutrients in plants are not mobil.
Mobil nutrients are nitrogen, potassium, magnesium, phosphate, chlorine, and molybdenum. Quick not Chlorine is needed in small amounts for plant goth. Plant typically get chlorine from safe chloride salts. Chlorine gas used to sterilize drinking water however will damage plant.
While potassium is often sighted. However any mobile nutrient can cause holes in leaves. I doubt you have a potassium deficiency. Leaf zone only has iron and potassium. The colorization of tap water often results in chloride salts in tap water so that is not liikel in my opinion. Molybdenum is one of the least used nutrients in plants probably unlikely unlesss you are using RO or distilled water. In my opinion magnesium is much more likely.
I would check your nitrate levels if you have measurable nitrate, nitrogen is unlikely. You could also get a phosphate test kit. Also monitor your Gh.the GH kit detects calcium and magnesium. How much water do you change out and how often. It might be possible to fix your problem by changing more water and doing it more frequently.
