Thats funny this guy would say you should grow these plants because Myrios, Egeria and Elodea are all listed as invasive species in many states across the country. There are several common plants that will grow in moderate to hard water, I don't think thats the question here. What Bert is talking about is the affects of hard water on plants in general and how to deal with it. There are quite a few plants in the hobby now that are considered soft water plants. Some may adapt to moderately hard water, but struggle at best in what Bert describes. I agree that the most ideal over all is somewhere in the middle. The age old question is how beneficial is it really to try and change your parameters? Once you start messing around with chemicals and buffers do you end up creating different problems than what you had in the first place?My experience is mostly with invasive's like hydrilla which you don't want to use. I know that Vallisneria does well in alkaline, hard waters. I think Myriophyllum and Bacopa do Ok in hard waters too. Some aquatic plants can absorb the carbonate salts and strip away the carbon from them, and use that as their carbon supply. The list of plants capable of doing this includes many that do very well in aquaria, including Ceratophyllum demersum, Cryptocoryne becketti, Echinodorus bleheri, Egeria densa, Elodea canadensis, and Vallisneria spp - all popular and easy to obtain species. If you have hard water and don't want to be bogged down with carbon dioxide fertilization, then these are definitely the plants for you! Admittedly, some of these plants are fussy in other ways. Echinodorus bleheri, for example, needs a rich substrate and good, strong lighting, but Ceratophyllum demersum and most of the Vallisneria are adaptable and easy to keep. If you want to keep live bearers, then Ceratophyllum demersum is difficult to beat as a floating plant that provides a refuge for newly born fry. Egeria densa, on the other hand, is a sturdy, fast-growing species ideally suited to subtropical tanks. Vallisneria spp. are perhaps the most versatile aquarium plants."