What can I add to my nutes late flower for increased yield

A top quality light will get a good yield .Blurple light is outdated now. A good white light full spectrum will usually get you at least a gram per watt. That's what I go by . I use 300watts and aim for 300gram yield. For better quality bud I like canna boost and pk13/14 in Coco.

Yeah grow a photo period strain instead lol autos are yet to catch up to the yields of Photo period strains yet they are close but not quite there :) My best advice lol Sorry that answer is a bit of a cop out from what you asked but your best bet would be adding a PK booster but I would go for an organic version of this if you want to better avoid an over feed :) another way to add more weight is to harvest late you will find flowers will dense up right until they die so if you leave them an extra 3 weeks you can imagine how dense they will be you will also get fresh bud growth which will mature and add to your yield though dont take it too long as she can self pollinate and get a few seeds if left too long :)

Light is the answer. You need a very good LED or an HID. And what UK told you. Autos do not yield the same as photos.