You say that you have always let the water stand to adjust to room temp? Am I right? That would rule out shock from watering with cold water.

The bit about Zinc defficiency and galvanised nails. Well, I just lifted this from somwhere else on the net. I dont know how many nails or how to distribute them in the soil and I would be more inclined to get a bottle of micro-nutrients and use very sparingly. The metals should be readily available to the plant in a solution made for plants.

I would be inclined to change nothing but the water you are using for a week. Every day... note down any changes like new spots. See if the problem is slowing down. Most likley the affected area will not repair itself so its new damage and new growth that you want to keep an eye on.

If you add a bit of this and a bit of that and change a bit of the other, you have no way of knowing what sorted the problem. You will likley be growing weed for years to come and I would love to find the cause of this problem because its so damn strange.

Your pic may be featured in posts for years to come if you can pin-point the cause of it.

Don't get dis-heartened because there is a problem... u are learning every day and it will pay you off ten fold further down the line :dance: