I bought fish eggs and put them in the tank but nothing happened. Is there a limited number of fish you can have in a tank? Is there somthing special you need for the eggs to hatch?

You probably tried to hatch the eggs in a tank that was already full. The eggs will hatch fine if there is room in the tank for them.

you were right .I counted my fish and I had 17. I'll buy another tank.

I already bought all the tanks but there is still not enough space for my fish - even the sale tank is full!

so delete some fish
that are taking space and you dont some fish

Selling is ALWAYS better than deleting, i find.