Honestly- and I'm wondering if hukit will agree, and I'm just getting started in NW cichlids with a 150g and my stocklist is, so far- 1 pair gold cons, 1 Dempsey and 3 pacu (only raising them till 5-8 and then turning them in for another 3 moderate sized pacu), and I don't inches thin inches k my copper veil oscar will behave well enough, lol- I rescued 5 baby red belly piranha and figured 90g for a couple nights while I fixed up 55g bowfront for my oscar and his buddy, a lava red cherax lobster- piranhas were 2-3 inches, I didn't think a tight school of 5 of these would be that much of a threat for my then 5 inch oscar... I was right :-( my oscar and cherax worked together to take out 2 of them- the 'nippers'- over night... My oscar is now about 7 inches and my cherax is 8 inches- however- my Dempsey (just a 1 inch baby, more like 3 now that I've had him for a week), my pair of cons is about are about 4 inches and my pacu are about 5 inches, piranhas have been rehomed and I don't dare put my bully oscar in there- not until the others grow a little bit bigger and maybe gain some aggression- I've been warned about when my breeding pairs' fry are free swimming, though at my lfs they had a free swimming batch of fry and were in a 40b with a few pink cons and they stayed in the corner with their cave and plants around them- I got all the decor in their 'territory' from my lfs and set it in my tank the same as in the original from the store in the corner of my 150g and so far I don't think they have even seen each other yet, lol, and I'm concerned about when they are older if I try introducing my oscar and I'm wondering if my 6 mottled hoplo cats will be safe and am considering breaking tradition and trading out my hoplo cats when my clown loaches get bigger (I have 3 in with my SE Asian biotope, but they will get too big for my 60g)...
Long story longer, I'm running a tetra pond filter at 900-1200 gph and 2 AC110, for surface movement and 4 Fluval U3s midway down across the back and I know from my experience with my moms 100,000g river system and my 500g Mekong tributary section (29 inch mystus leucaphasis, redtail cat and, I can't help myself- 1 18inch red oscar, 2 (12 and 16 inch) tiger oscars and a 32 inch true giant gold gourami and several mystus sp- hi fin mystus) and I'm running 2
filtration required and I still have found that I have to maintain my filter sections and circulation units every other week...
My warning about stocking a 90g with as many of the territorial ca cichlids suggested is the amount of aquascaping required to create safe spots, 'homes' for these guys to call their own isn't for the faint hearted (or shallow pocketed)- that being said, along with that amount of decor and messy fish leaves soooooo many places for excess food, detritus and rot to hide and create problems if you're not careful to move all decorations and vacuum plants and substrate thoroughly weekly....
If I was using my 90g for ca/sa cichlids, I would honestly go for either one large centerpiece fish like an Uaru or blue acara or the likes and a school of hoplo cats or skunk loaches plus a couple rubber pleco
OR
A couple pairs of rams, a school of diamond tetra and a school of panda cories and 3 or 4 albino bristlenosed plecs. Granted, any 3-4 inch dwarf cichlids, medium bodied tetra and smaller plecs would work..
Just my opinion...