Originally Posted by kekon
very soft water (GH = 2) i had caused the following:
- exceptionally good growth of Cabomba and Blyxa Japonica (Cabomba had to be pruned twice a week)
- a bit faster growth of Didiplis Diandra
- almost all growing tips on Rotalas, Umbrosum, polysperma were stunted
- alternateras had horribly deformed and bent leaves, some specimens just died quickly
- leaves colors not affected by higher NO3
- very heavy pearling
- some plants didn't show any changes in growth and coloration; these inlcuded Glossistigma, Anubias
This describes my tank very well. My tap water here is pretty much gH <1 kH <1. I boost gH to 3 using a home made booster very much like Seachem's Equilibrium and with a Ca:Mg ration of 4:1 and a fair bit of K.
Blyxa and Limnophila grow explosively as does Hygrophila corymbosa 'kompact' but I struggle with stunted growth in most of my Rotala (R. mexicana, R. occultiflora, R. rotundifolia). R. macranda grows OK. Hygrophila polysperma also shows some stunting. I also notice that many plants in my tank tend to a greener colour despite being under metal halide lights. I have a narrow Echinodorus tenellus that many people grow as a nice pink/red, yet mine is mostly green. H. polysperma 'rosanervig' gorws green under the halides in this tank yet its a beautiful pink under a much lower wattage T8 flouro in another tank.
Based on your observations - I'm going to try increasing Mg for a bit and see if my Rotalas respond.