OK, finally I have found some information on this topic elsewhere. So it seems that GH is important for plants just for Ca & Mg content (a lot of plants seems to do well with 3-5 dGH). But many plants seems to prefer low KH (= alkalinity). Some plants require very low KH (e.g. Tonina, Eriocaulon, Syngonanthus, Ludwigia Pantanal, Ludwigia wallichi ... some don't do too well with higher KH, like Rotala macrandra/vietnam/nanjashan/hippurus ... maybe Eleocharis parvulus seems to do better under 10 dKH). So can anyone explain why most of plants prefer lower KH? Why higher KH bother/hinder them? I have 15 dKH, and I have to say that Eleocharis parvulus (dwarf hairgrass) doesn't grow very well ... althout I have quite a lot of CO2, EI ferts (35 mg/l NO3, 25 mg/l K, 5 mg/l PO4, 0.5 mg/l Fe + micro), good flow, and 70 umol PAR at the substrate. At the evening Eleocharis is pearling a little bit ... still the new leaves turn slowly brown after couple of weeks. Does anyone have a similar experience? Could it be because of high KH? My other plants like Pogostemon erectus, Alternanthera reineckii, Limnophila aromatica, Ludwigia palustris/repens, and Vallisneria ... all grow very well.
