Trying to save my 9 foot beauty just repotted and looking for further advice .

 

I just repotted my 9 foot FLF- I acquired it in January and it seem to be doing quite well all winter and I’ve been using your proprietary fertilizer and Watering about five cups water every 10 days-  last month with the warmer temperatures here the tree started to sprout some nice new growth at the top (about 7-8 new leaves)

but at the same time the lower leaves start to develop Brown spots originating at the center outside edge and serval leaves dropped and I have had to cut others. The tree was very tight in the original planter pot so I just repotted using the instructions from this site.  I did not observe any obviously mushy or rotten portions of the root ball. Just wanting to know if there’s anything else I should do right now after repotting? I plan to buy some of the root stimulator/rot preventer today-  Thanks! Drew