I did buy one kilogram of urea but I have yet to use it. Maybe I will experiment a little. Currently trying synthetic auxins (NAA/NAD) at around 10-9M (or at least I hope). My pH is also north of 7 and I am aware of the issues but need to look at a few graphs to gauge the danger or risk. Interesting, the water (desalinated seawater really) around here is also very poor in Mg yet high in Ca with but also soft I believe. Could not find any good kits and not bothered to test at the university (too many questions asked)
I do find some very interesting products around here, like this one: http://www.chema.com.eg/SpcialFertilizers.html
scroll down to Elodia* (sic) which reminded/lead me to this while searching about allelopathy a while back: https://docs.google.com/viewer?a=v&q...Ll0KOdPpBM2WQ7
Which coincidentally is also done in Germany! Those Germans love aquatic plants. I only read the abstract and skimmed the paper so apologies if it is not related.
I wish you good luck.