Trapa natans/water chestnut

I just acquired three large specimens of Trapa natans, from one of our
better shops in the twin city area.  I have placed them in a 3/4 full
75gal, full covers, to hold the humidity, a powerhead to help increase the
humidity and four 4' full spectrum tubes(48").  I am presently using R.O.
water with trace elements replaced as I saw fit.  Has anyone any further
thoughts as to what other things might help them to reproduce?

Karl R. Schoeler