Definitely get the GH test as my tap water is different to the website - my local area on the website is 17 but out of the tap its 13/14 so I'm at the upper end of quite a few common species now that were out of my reach before. At my last house on the other side of the city it was 19 - though I didnt really factor it in for those years and kept a south american tank.
The effect of keeping fish not naturally from hardwater in hardwater tanks is they build up calcium deposits in their body - essentially kidney stones and their lifespan shortens quite significantly. One member here kept a school of neons and typically had them 18-24 months then started using RO water to soften it and they are over 5 years old now, in other fish it can be less so and others even more extreme but its typically a long term consideration. They will also be more prone to stress so disease can really take hold faster and harder than if you had fish matched to your tap water.
I look at it quite balanced, for example if you see 100 neon tetras in a local store and most of your region is hard water the majority of them are going in hard water. So for me if you tick 9/10 boxes other than water hardness in terms of compatibility, tank size, diet, water changes, maintenance etc I'm not going to tell you not to do it because you would a great option for those animals rather than the risk of going into an uncycled tank, no maintenance, small tanks, end up as prey for bigger fish etc.
There are other fish out there, I've been reading up on it a lot and my basic rule of thumb is look for fish from places with mountain fed streams like Vietnam, Laos, Burma/Myanmar and avoid places that have swamps and long winding rivers fed by flood plains, Sumatara, Papua etc. Fish distributed in mountain streams will come into contact regularly with water that has been mineralised by the bed rock - Vietnam and Laos in particular are know for limestone beds, Myanmar is a mix but thats what feeds Lake Inle as an example. Some Stiphodon Gobies are from harder water, some Sicyopterus (spelling) species are from harder water and a few others. Empire Gudgeons could be a good choice, though they span Asia into Australia so not sure if thats out of your scope? I'm not sure where they are from but some Panchax species are harder water like the Golden Wonders and some halfbeaks are too, I think you mentioned them at one point?
Other options from outside South East Asia are things like Rainbowfish, Central American and Rift Lake Cichlids too - though Rift Lakes are not a community set up. Some Synodontis species from Lake Tanganyika too.
Wills
