With that 90 gallon tank it may be a problem. Neets are very aggressive and with that size tank it increases the neet aggression. Meaning, the other fish will find less space to avoid the Neet. He will nip fins; they have a way of making your other fish look ugly. I would be more concern with the female Festae then I would the Jack Dempseys. Jack Dempseys a little shyer then the Festae. The Festae will be more personal and therefore more vulnerable to get the fins nipped. While the Festae is paying attention to you and begging for food, the Neet will sneak and nip her fins. The Jack Dempsey is more likely to pay more attention to the Neet. Of course this is just my opinion. I have had them before, and had the prettiest Festae that you would want to see, and the Neet went to work on his fins, although he could beat the neet, he didn't pay much attention to him, he paid more attention to me, and the neet would sneak him... Although I do like the neets also, but they have a tendency to make your show fish look ragged...