if you have a very compatible pair, it can work in a 90, a bit cramped, and it wouldnt be in the fishes favour (is any tank to a fishes favor?) but it can work just fine.Marc280106 said:A 90g is insufficient for a breeding pair. Otherwise good advice.
As stated, the male will be able to fertilise the eggs if they have been layed next to the divider. Another tecnique commonly used is to cut holes in the divider, for the smaller of the two to escape when/if needed. You can rmove the divider as the female is preparing to lay the eggs, but when doing so be sure to supervise as they can inflict a great deal of damage in a short period of time.