Kesy,

Stuttgart has
been grown for the past 25 plus years. It has dumbfounded both the professional
and amateur grower. The non-chlorophyll producing areas of the leaf are white
and ultimately desiccate (turn brown). IMO I think we are dealing with a
genetic deficiency that is not advantageous for this cultivar. There have been
rare times when it produces beautiful plants for a period of time but
replicating those conditions seems to be very elusive.

I cannot
offer much about the heated fish tank idea. You do not mention the location or
temperature to which the plant containers are exposed. Keep in mind that
growing in semi-shade in the summer months does provide more hours of daylight
that will impact the growth in the winter months.

Kent