i've got 5 species of plants in my nano. 3 of them are stem plants. supposed to be FAST growers.. ludwigia repens, water sprite, rotala indica. they have 9hrs of light a day. i dose excel and ferts every other day. i do ~%50water changes 2x a week. these plants (and the rest) WILL NOT GROW! i cant even get roots to develop on the rotala. the water sprite just sits there. nothing is dying, just seemingly dormant. whats the deal?