That is not goumi based on what I have identified and eaten at the arboretum near me, what I have outside and a quick google search of goumi leaf.
Based on those leaves that you posted, if its a fruit tree it would be mulberry but it could also just be a "weed plant".
As for you possible 'over-feeding' the plants. I would flush out the soil by submerging the pot into a huge
bucket. The salts will 'dissolve evenly' between the pot and bucket of
water, thus lowering the concentration. You can then throw away the bucket of water with all its dissolved salt. If needed you can repeat this process a few times.
Iterations are fine, we don't have to be perfect
My 2nd Location:Florida HardinessZone:10 AHS:10 GDD:8500 Rainfall:2in/mth winter, 8in/mth summer, Soil:Sand pH8 Flat