since you are a new frogger, i would recommend each species has their own tank. while multispecies tanks have their appeal, they should only be done by keepers with many years experience. those that know the species kept inside and out. their quirks, characteristic and whatnot. you need to inhibit problems BEFORE they happen. also, a large tank is required (90x50x60 is not really that large a tank) so that they can be broken sight lines, plenty of hiding room and plenty of room for frogs to establish their territory. best bet would be to split the difference and get each species a 45x45x60 (i think that's the metric equivalent to an 18x18x24). it will take up the same space as the one you wanted, but will house both species safely and without the risk of cross contamination.