I potted my pink dipladenia hanging on the rails outside my balcony and it was flourishing beautifully for about 2 months. Foliage grew and flowers blossomed every day. Then suddenly the leaves started getting brown around the edges (no yellow nor gray nor little holes. Just dark browning) making the leaf look and feel "weakened" and eventually falling off (before turning fully brown or dry. Still greenish but softer and weaker). Suddenly the plant lost most of its volume. It still blooms but the flowers last less time and some fall off before blooming.
The browning is not in one particular area, but it appears on random leaves around the plant. No bugs to be seen anywhere. I tried taking off the affected leaves but new ones appeared by themselves.
I tried fertilizing for the first time. Nothing changed except some new flowers appeared.
Does not look like blight. And it kinda looks like burning from the sun, since it does get a lot of hours of direct sunlight and im in a pretty hot area. But that wouldnt explain why only the edges look burnt or why some leaves that are more hidden are also browning.
The pot has 4 holes under it and i water it when the soil is getting dry but not bone dry, and I let the water flow through until it flushes out of the holes.
Am i doing anything wrong?