28 c is very hot is that not over 80 ?(thats seems a bit high, no?) whats your humidity and air flow in the room is your plant getting fresh air? i used canna for my last grow and found that it was easy to over feed with , what about folar feeding (i only folar feed under my leaves!) remember the plant dos'nae use a lot of N during flower so fan leaves die .. are you using the lift the pot method for watering ? it has to be the best thing i've learned so far ! cos not all plants are the same, some like more or less food than others , are you letting the roots dry enough before you water?, i would use nowt but P h'd water for a few day's and if its the feeding you'll find out quick enough .... good luck pal ...may your grows be healthy and DANK