I think it basically comes down to research, research and yes a bit more research. The charts you picture show just how much we should research and not just assume!

I think too many just see a pretty fish and don’t think too much beyond that, (then go online distraught because their pretty fish keep dying)!

Personally, I don’t need biotope “exact” (eg I am going to be putting dead reef rock in my mbuna tank - and some plants). However, with the exception of the synodontis, all the fish will be from Malawi.

 

So what does being biotopically correct mean?
To me, it means water parameters are checked with a little research, where the fish we keep are collected, or endemic.
It may mean photographs of the substrate, and habitat are taken, or researched.
it may mean currents and flows and temps are studied, and emulated
and sometimes even the terrestrial surroundings, to see how these species live nature (or not), if are they shaded, or if full sun blankets their habitat in nature.

Not that we all need to collect and get pics, and perfect substrate, but these days….but
with water parameters known, and available with the flick of a mouse, data is available.
The Rio Negro has pH if 4 to 6, water is soft, and inundated with tannins.
Lake Tanganyika has a pH of 8 to 9, water is mineral rich.
Water west of the Andes where GTs and festae are found, has an average pH of 7, but is also more alkaline (unlike the 6.5 and below pH, soft mineral poor waters of the Amazon).

So¨ you may ask, what relevance does this have to the tiny puddles we force our fish to endure in closed constantly recirculating box systems?
To me it means, we, as custodians of the fish we keep, should provide similar and adequate water parameters, those they would exist, and are evolved to live in, to their natural habitat, if at all possible.
Parameters such as pH, hardness, nitrate, temp, and flow rates,…….whatever we can do to emulate an ideal natural setting.

But does it mean we should chase water parameters?
Actually no…..but it means choosing the correct species, that match our tap water.
but It means if we are blessed with low pH, soft water,
those are probably the species we are meant to keep. (such as S American Amazonian's, west Africans, or S East Asians)
or
if we are blessed with hard, high pH water, fish from the Rift lakes of Africa, or high pH waters of Central/North America would be apropos.

It is (of course) possible to fight our water chemistry, but that means essentially, putting on a chemists hat, and doing continuous water parameter tinkering, and adjusting to keep the our fish healthy.
And not figure, that 50 or 100 years of aquarium breeding and husbandry, negates several million years of evolution to a specific habitat.

But what if I want severums, or Cardinal tetras, yet my water is hard and has high pH?
There are reasonable facsimiles of species, adapted to many waters around the world to choose from..

Above are Etroplus suratensesus, very similar ito severum, in that it is a vegetarian like most severums, get the same size, and prefer to live in shoals (like severums do), come from similar warer temps, but yet come from the higher pH, hard water of India, and can even handle brackish conditions.
I have seen posts on cichlid sites occasionally mixing up the two old and new world cichlids.

Above are Roeboides and Astyanax tetras found in the hard high pH waters from Panama to Mexico…… maybe not quite as electrically colored as Cardinals, but would you rather have tetras that live, or die at the drop of a hat, in high pH hard water.
Cardinals are endemic to pH waters of about 5, the ones above pH above 8.

 

Water parameters are one thing, and a simple one at that, but another extremely important issue is the biology of the fishes themselves as regards their behaviours and interactions. Both conspecific and heterospecific cichlids communicate with each other in many ways, but they don't all 'speak' the same 'language.' A particular posture or gesture may mean one thing to a Central American cichlid, but something completely different to a cichlid from one of Africa's Great Rift Lakes. And as we all know, miscommunication can be lethal.

But even species that share habitat in nature are often poor tankmates in captivity. For example, members of the tribes Ectodini and Tropheini occur together along many rocky shorelines of Lake Tanganyika, and yet they cannot be kept together in captivity because they generally don't have enough room to get out of each other's way. This invariably leads to conflicts that cannot be resolved in the limited space of an aquarium.

Even closely-related species that live together in the wild may turn out to be poor tankmates. For example, although Tropheus are generally kept in single-population species tanks in captivity for fear of hybridization, some Tropheus species do occur sympatrically in the lake. One example would be Tropheus sp. 'black' Ikola and T. annectens Kalugunga, which cohabit a small section of the eastern shoreline. I had kept these populations separately for some time, but when i tried a mixed population tank the T. sp. 'black' Ikola flourished and spawned regularly, whilst the T. annectens languished and didn't spawn at all. Back into separate quarters, and everyone is happy. Another reminder that our aquaria can never recapitulate the natural environment in which these fishes evolved, so it falls to us to be vigilant about their welfare in captivity.

 

Great explanation!

 

Although there are convergent evolutionary species from various water types, that inhabit similar parameters all over the world that seemingly ¨could¨ in theory, be intermixed in non-geographically correct ways,
they may really ¨not¨ actually coexist?

These days the importance of keeping only species together that from hail from the same waters, over natural substrate, and even with the terrestrial surroundings has become an important part of my biotope obsession.
Because of where I now live (Panama), to get the species I want to keep, I must collect them myself. In Panama native species are not ¨legally sold, (except to be eaten), and as an aquarist, those are not the species I want.
One of the 1st things I did when moving here, was to check my tap water water parameters, ti actually get a take, of which fish species work, with the water I had to deal with.

So when I collect species, water parameters of the the rivers, or lakes where I collect are tested to be sure what is collected, actually survives in a healthy state. If my tap water doesn´t conform, even if I spent $200 collecting, those fish are not kept.
Most rivers east of Panama City, match pretty well.

Its interesting that the nitrate levels in nature are so low, to keep a concentration similar, my water change routine has had to be kept at at least 100% per week (abbout 40% every other day), and large scale planted sumps to consume nitrates between water changes are needed.

I am no longer interested in the generic mixed mutt African´s, or illegitimat-species like fake Vieja, and ¨especially¨ not, those man made designer un-legitimate species, color morphs, and franken-fish, those most often sold these days in LFSs here, and around the world.
If ¨I could ¨acquire species such as any of the genus Stomatepia, or the fresh water sponge eater Pungu maclareni from Lake Barumbi mbo, I’d gladly set up and extra biotope from that lake.

Or a riverine , rheophillic tank for Heterochromis multidens, with Teleograma and Steatocranus cichlids, Phenacogrammus, tetras , and Garra algae eaters also from the Congo River as tank mates,
but these were hard enough to access in the US when I was there, and are an impossibility here.

 

I am pleased the variety of species here in just eastern Panamanian rivers alone, is amazing, although I have only located 3 species of endemic cichlids so far, they do not disappoint.

And to simulate varied habitat in the limited tank space, there are a few higher flow areas, areas more open, and sunlit, others shaded from above and below.