Usually jellyfish are at the end of July - the first half of August, when the water near the coast is warmest (multiply by sail).

In the second half of August I can not guarantee that they will not be at all , but the probability of appearance is significantly reduced. In addition, "full of jellyfish" - it is, nevertheless, greatly exaggerated. There are, yes, you need to be careful when swimming, but the sea does not swarm at all. In addition, in Tunisia pharmacies are sold special creams, "repellents" from jellyfish; they happen to SPF and without it, and in case you were stung after all, creams quickly heal the burn. So it's not so scary :))