@MaryJaneUSA, If it starts from the bottom leaves, then itโs calcium- magnesium problem. It could also represent fungus rust. If this is true, then you need to separate all your nearby plants because it can spread via spores. But your plant looks healthy.
Either itโs cal mag issues or your pot isnโt draining well and you may be overwatering
I had this issue before and I think your right has something to do with C-M. I increased the amount of calmag slightly and raised my ph to about 6.4 and that reduced the rate of leaves being affected but didnโt entirely solve it. Was late flowering last couple weeks I had this issue.