For the first time in 15 years...

[duanes]

It it is usually explained that the fish itself can tolerate different water parameters as an advanced species, and i agree with this.
But.......
I come at it as a microbiologist (ret.) and believe that it is the microbiotic organisms that control the outcome, in many aquarists tanks.
Most microbes thrive in very narrow pH or hardness ranges, some cannot reproduce if pH is slightly acid, or not enough calcium or nitrate is available. When I grew pathogenic bacteria in the lab, pH of growth media had to be in a certain range 7.2 (+/_) 0.2. If that media was even more than 0.2, it had to be tossed.
For a fish that has evolved to live in low pH water, resistance to microbes that need pH 7.00 to 8.00 is not required, so when that low pH fish is forced into high pH water, those high pH microbes are able to infect with impunity because of low fish species bacteriological immunity.
Add to that "lack of immunity" to the average aquarists tanks normal elevated nitrate level, and you get the plethora of HLLE scarred oscars, sevs, Uaru, and other South Americans so often seen in the Disease section.

 

[twentyleagues]

Cichlids that work with severums
Green terror
Convict
Parrot
Texas
Festivum blue acara
Oscar
Geophagus
Chocolate cichlid
Uaru
Jack dempsey and all color morphs
Pikes
Salvini
Vieja
Peacock bass
Firemouth
yellow jacket cichlid

This I dont agree so much with. For the reasons listed below. And actually looking at some of the fish id say might be a mess aggression wise too.

While I agree that many of the South American species listed above work with severums, I disagree with many on the list of what is said to work, and although many severum are aquarium strain and superficiously adapted, they originally are evolved to live in soft, less than nuetral pH waters. While many of the Centrals listed come from high pH, hard waters of Central America,and Mexico.
And the aggression level of many of those Centrals is much more heightened and territorial than their South American cousins.
And although you may not experience problems right away, down the road, health issues often show up as HLLE and other water parameter stress problems.

It it is usually explained that the fish itself can tolerate different water parameters as an advanced species, and i agree with this.
But.......
I come at it as a microbiologist (ret.) and believe that it is the microbiotic organisms that control the outcome, in many aquarists tanks.
Most microbes thrive in very narrow pH or hardness ranges, some cannot reproduce if pH is slightly acid, or not enough calcium or nitrate is available. When I grew pathogenic bacteria in the lab, pH of growth media had to be in a certain range 7.2 (+/_) 0.2. If that media was even more than 0.2, it had to be tossed.
For a fish that has evolved to live in low pH water, resistance to microbes that need pH 7.00 to 8.00 is not required, so when that low pH fish is forced into high pH water, those high pH microbes are able to infect with impunity because of low fish species bacteriological immunity.
Add to that "lack of immunity" to the average aquarists tanks normal elevated nitrate level, and you get the plethora of HLLE scarred oscars, sevs, Uaru, and other South Americans so often seen in the Disease section.

These I agree with!
Sorry had to clear that up. At least in my head if not anyone else's. Carry on!

 

[neutrino]

Similar to Geophagus, Symphysodon (discus), Pterophyllum (angelfish) and others, Heros species cover a wide area in the wild and vary in pH preferences and tolerance. Take discus species, they can be found in pH ranging from very low to 7.8, yet you continue to see people generalize and insist they all must have lower pH.

Severus and Inirida are blackwater species. I haven't done blackwater tanks in years, so I have yet to keep either of these-- Jeff R offered to do me a deal on inirida last year, but said in his experience they're susceptible to HITH without soft water, so I didn't get them. I've seen the same said for severus.

However, a number of other Heros types do just fine in neutral or higher ph-- I say this from experience and/or people I know who've had them. Just how high depends on which type. Notatus and liberifer are fine with neutral or a bit higher, not sure of their upper limit. Rotkeil, common green severums, golds, and efasciatus from some locations aren't fussy at all with the upper 7s, maybe 8-ish. Among my rotkeils was one purchased as wild, which lived 15 years in pH varying from the upper mid-7s to 8 with perfect health all the while. I've had a similar experience with other types-- but as I say, this excludes severus and sp. inirida.

All of this assumes clean water, appropriate temps, good food, etc. Bottom line imo is while many Heros types are reasonably adaptable, there are exeptions and if you're considering one of the uncommon types, I'd suggest researching or asking about their specific requirements.