I absolutely love apistos. They are a fish that are somewhat difficult to find the "balance" with. I think there are absurd misconceptions about them out there.
Dalto's recommendations seem great. I have kept around 15 species, and am now keeping 12 species in 14 tanks.
I would also start with Apistogramma cacatuoides, as they come from environments with constantly fluctuating hardness. They are also very hardy if kept in the conditions that Dalto outlined. I have kept and bred a few different species now, but I really love all Apistos. If you can ensure that they get plenty of frozen/live/filler-less prepared foods, start out with good stock initially, and keep their water clean, you should have little issues.
Okay besides your opinion on them not needing an established tank, you pretty much said everything I did besides you added the factor of water hardness. Just because you've kept over 30 species of anything doesn't mean a thing if you can't keep them alive.. most apistos I know of live to be 5-7 years old depending specific species. That's either a lot of aquariums and major money or you've kept fish for years and years, some of which you must of had species of before being common in the trade.
I personally have kept apistos in tanks without filters but with a high plant load. In this way, the fish excrete waste, plants use those wastes to grow. Often times, I take a tank, add some sand, a layer of floaters, some driftwood and leaf litter... and I have a suirable habitat for a pair or two of Apistos.
You may have had issues due to hardness. My water is soft, pH ranging from 6.2-6.8 and hardness level at around 150 TDS. Portland tap water baby! All apistos that come into my tanks are acclimated to these conditions, including the blackwater species that are associated with TDS below 10 and pH of at 5.5.
Honestly, the biggest problem is inadequate diet. For that reason, I keep them in species only tanks. Tetras are much too vigorous and eat quickly, so I often do not include them in Apisto tanks (they steal all the food
)
Here is one of the males I got from my first Apistogramma spawn ever. This was a picture taken early June, after 3-4 months of growth.
Species I keep now:
Apistogramma iniridae
Apistogramma hongsloi
Apistogramma sp. Totaya
Apistogramma sp. D50
Apistogramma bitaeniata "Rio Jutai"
Apistogramma cf. ortegai
Apistogramma barlowi
Apistogramma sp. Abacaxis
Supposed to receive a few new species very soon...
I keep my favorites and sell off the rest. So far, the top two on my list in terms of quality are Apistogramma hongsloi and Apistogramma iniridae. In terms of choosing favorites, it would be between sp. Abacaxis, sp. D50, or iniridae. All three are pretty, and have awesome behaviors. I love waking up in the morning and seeing my iniridae males flaring at each other... it's a sight to behold.
Good luck! If you have any questions, feel free to PM me, or if you want pictures, just ask!
Shane