Hi Lily,
You are in Zone 11 ?? That must be pretty tropical for you to be growing zinnias. My outdoor zinnias are all frozen and dead here in Kansas. I take it you are in the Northern Hemisphere.
Are those zinnias growing in pots, and if so, what is the nature of the potting mix? I see at least two problems in that second picture. The dying tip could be a foliage disease. I would suggest snipping off the outer third or so of that leaf, just to make sure you "got it all" and discard that in the trash as a "biohazard".
The top picture has a leaf that looks like something took a big bite out of it. Both pictures show malformations in the newly forming leaves that could be a symptom of a calcium deficiency. Some nutrient deficiency for sure. What product(s) are you using to supply nutrients?
I grow and breed zinnias as a hobby, and I am still learning things about them. And that learning process will continue indefinitely. So I don't classify myself as an "expert", but I am interested in zinnias. I am attaching a couple of pictures of some of my "home hybridized" zinnias as an example of what you can accomplish beyond what is available in commercial zinnia seed packets.
It is amazing what you can accomplish if you "be the bee" and do your own cross-pollinations of your zinnias.
If you have any more pictures of your zinnia leaves, it might help to post them. I am suspecting a nutritional deficiency.
ZM
