Rust spots
could also mean a calcium def, but it's also a part of a K deficiency- I marked this leaf on Thursday, and I've been watching it since then- it hasn't gotten any worse in 4 days, in fact it's gotten a bit greener, and that's how I can tell the Purpinator is working- it took 5 days from first application before any improvements were seen, so, even in a SIP, it doesn't happen very fast...but it did happen.
So, your Crescendo may stop with the rusty spots by mid week, if she behaves like the ATF did..
In case you wonder, I've been using 15ml of Purpinator per gallon, with every watering- they say you can use up to 30ml, but that sounds a bit hot to me..
From this morning: Not pretty, but not dead, either..