I live in the Shenandoa Valley of Virginia, where the water is also very hard. Mine usually tests at around 300 ppm. I have several species of tetras (buenos aires, black neon, glolight, and rummynose), as well as rams (which have been doing well except now the tank has ich because of my stupidity), which all prefer soft water. I don't think that there is a problem with keeping fish that prefer soft water in hard water, except that it's harder to breed them. If the fish have come from soft water, and you're going to be keeping them in hard water, you may have to acclimate them VERY slowly. However, since all of the pet stores local to me are on the same water system, they have water that is just as hard as mine. So if I see something I like in one of the stores, I usually wait a week and then buy it, since it will be acclimated to our local water by then (I suppose). I think that the water in Florida where a lot of the fish sold in the US are bred is hard, so unless you're getting fish straight from the wild, I don't think you'll have any major problems.