Cockatoos are probably the most forgiving of the apistos .
I have had my male for 6 months , his mate died about 2 months ago . I think the male harassed her to much .
That said it is best to have about three females per male , bare minimun of 2 females .
One to one is not a good combo , the males get twice as big [ maybe even more ].And the females need a break from the males advances .
Also a good amount of cover should be provided , in the form plants , caves , things they can hang out in and rest .
My PH is just on alkaline side of neutral , and my water is slightly hard , the temp is 78 Fahrenheit, the fish is thriving , when the female was alive they bred many times and even herded fry around my tank [ check my Sig ] . After the last batch was eaten by the tanks inhabitants , the male just rode her into the ground , 1 or 2 more females may have made the difference........ the trouble is most shops will only sell pairs .
Now I hear they do better in softer and more slightly acidic water as well .
not sure what others keep theirs in tank wise
Also try searching GOOGLE that's what did and still do .
By the way the apistogramma cockatoids is a very good choice , as long as you can swing the price these little fish bring in , you'll love keeping them .
a sponge filter[ size appropriate ] is good as long as you do regular water changes , my 70 gallon has an under gravel filter driven by power heads , that's all , been that way for 3 years . That and the plants are my filtration . I change 20 to 30 % of the water each week .