DEFREESE AQUARIUMS

Seeing that was your only change is a good indicator of the issue. I would definitely would consider fertilizer and if you still have the issue, I would try dosing potassium or macro fertilizers and see if that helps. Good luck

On the one java pictures it appears to be hair/fuzz algae or BBA. Hard to tell at the angle, below are some videos that should help you out. Check out this video

You can run a small, I run the small in my 10 gallons. You could also add Co-op's powerhead on the sponge or one with a adjustable flow control to eliminate or reduce the dead spot as well as even out the temp throughout the tank.

The flowers smell good almost like chamomile scent to them. If you have a few you really can smell away from the tank. Looks good!

Not sure what light you are using, but if it's too bright you can be burning the leaves causing them to die. But as others have mentioned in some cases it just a lack of potassium.

Well hello there Bob