thanks for your answers!
Sorry I missed in my post, to mention that I tried already to limit the guests capacity to 3000, but then I loose to much money :S.
Make sure you have donation boxes at every single habitat and exhibit, near where people gather to view the animals and that you have ATMs scattered all over the zoo so people don't run out of money no matter where they are. And lastly, control your biggest expenses, which are feeding costs and staff salaries. Do not over-train your staff, do not have more staff than you need, and limit the population of animals that are super-expensive to feed.
For my zoos, I've limited visitor count in all of them, and money hasn't been an issue at all. Most of them are making 100,000+ a year profit.
Staff is a big one that I think people over-do. I only use 1 or 2 vets in any of my zoos, even the big ones, and I don't train any of my keepers past 2 stars unless they work on a habitat that is really big with many different animals in it (then I'll take them all the way to 5). Also you don't need one keeper for each habitat. A single 2-star keeper can handle 2 or 3 normal sized habitats. Because they do need breaks though, what I do is assign work zones with 3-5 habitats in them, and assign 2-4 keepers to the work zone, based on what is needed to keep it clean and animals fed. The main key is to have the keeper hut and a staff room both nearby and centrally located, as those are cheaper to maintain then keeper salaries it makes sense to have them all over the park as needed.