I see in the shops various tetras that are raised in hard water,
Almost certainly not true. Tetras have to be bred in soft water. Lots of shops will tell you fish are "adapted to soft water" but that often means very little. Most of your common tetras are either wild-caught (for example Cardinals) or bred on farms in soft water (as with Neons). Fish farms can't be bothered to breed hard water varieties of tetras because there's no point. Tetras need soft water for their eggs to develop, and why waste years and years selecting for the occasional Neon that breeds in slightly harder water than the others when you could sell a million regular Neons every year?
If you go to one of the better aquarium shops, you will see signs up on the tanks stating whether the fish needs hard water or soft water. But less reputable stores will simply *tell* you what you want to hear, that the Neons and Cardinals and Diamond Tetras are all "hard water ready" fish good for your local tank. They may well survive a few months, even a year or two in hard water. But their colours will never be as good as in soft water, and their health and lifespan will never be as impressive.
Bottom line, if you have hard water, either skip tetras, or choose species known to thrive in hard water -- such as X-Ray Tetras, False Penguin Tetras or Serpae Tetras. In the case of X-Ray Tetras for example, these actually do come from coastal habitats that can be quite hard by South American standards, and occasionally even slightly brackish! Even if they won't breed in hard water, X-Ray Tetras seem to live long and happy lives in it.
I hear of angelfish, oscars and discus that can live at ph 7.5 to 8…
Cichlids are a bit different because they're (mostly) easier to breed and (mostly) more adaptable than the majority of tetras. You are absolutely correct that standard Angels and Oscars will do perfectly well at hardness levels up to around 20 degrees dH. I wouldn't keep Discus in water that hard, but farmed Discus will certainly thrive around 10 degrees dH, pH 7.5, which is much, much more alkaline than wild Discus.
I understand wanting to keep these beautiful fish even if the water isn't suitable, but I really don't believe these fish are happy in water that isn't suitable. Shouldn't we make our best to offer them the best environment instead of going against their nature for our benefit?
You are quite right.
I mean, nobody's breeding polar bears that can live in the tropics for tropical zoos, are they, they make their best to give them their own environment.
Again, you are quite right, and the analogy is a good one. Let's say there's a zoo in Southern California that keeps Polar Bears. While the bears might be okay, it's not their normal environment and they will surely be suffering from heat stress. But there is a big difference between bears (which are mammals) and fish -- fish can't adjust their body temperature, whereas bears can, just as we can. Fish aren't as able to tolerate wide ranges of environmental parameters, and you tend to see fish living in quite narrow sets of conditions, whether we're talking about temperature, water chemistry or salinity.
I believe I've made a hash of what I wanted to say, I hope it comes through...
Made sense to me!
Cheers, Neale
