The carrying capacity of two 75 gal does not equal to one 135 gal when it comes to large CA/SA. The tolerance of cichlids varies greatly with the size of the tank they house in. A smaller tank makes mildly aggressive fish less tolerant, and a bigger tank makes aggressive fish more tolerant. A 75 gal can house no more than one 14" plus a few smaller fish. A 135 gal can house four mildly aggressive 14" plus a few more smaller fish, twice as many as two 75 gal can house. Certainly, for super aggressive CA like Flowerhorn, even a 135 gal cannot house more than one. On the other hand, even a mildly aggressive synspillum cannot tolerate another similar size Vieja in a 75 gal.