Aponogeton mad. has small leaves

After considerable growth when I first put these plants in my aquariums
the growth rate is now much slower than I would be happy with. (So
much for vermiculite and worm poop ;-) The substrate appears to be
satisfactory for other plants but not producing the desired results
for the lace plants.

I had reduced the temperature in the MH tank where both plants now
live to about 75d F. This appeared to stimulate new leaf production
on both tubers however the new leaves are not growing rapidly and
appear fully developed at about 4" in length.

I think the plants should still be in a growth phase where they are
metabolizing and storing energy in the tubers however the small
leaves probably cannot perform this efficiently.

This phase of small leaves is similar to what occurred with my
previous specimen which lived about a year and a half. They really
don't like being transplanted I suspect. Smaller and fewer leaves
until it stops entirely.

Assuming lack of nutrients the options are:
1) insert plant nutrient tablets in the substrate around the two
2) plant small crypts around them to increase root infusion of
nutrients into the substrate.

Assuming temperature factors: raise or lower temperatures more

Duration of lighting: alter photo period.

Water chemistry:
- increase water change frequency
- raise/lower pH, Ca, Mg, K, P, nitrates, Fe

- new tank, all lace plants??

I have lots of baby Platys, 8 Otos, 1 Farly, 2 corys, 1 flying fox
and pregnant mother Platy in a breeding trap. Not a heavy fish
load for a 75 gal tank. I feed sparingly.

I aim for pH 6.5, CO2 about 15ppm (soft water)
Haven't measured Fe recently but dope it regularly. Should be about
.1 ppm I think. Ammonia, nitrites not measurable. No nitrate kit.
(I know, I know) I change about 20% about 3 wks or so.
Using the ?? plant supplement and iron supplement regularly.
Perhaps it's not enough ammonium or K. It's hard to increase my
fish load without endangering the fry. Lighting is 250w MH on
12hrs. Guess I'll measure what I can tonight and report back
but somehow I don't think that's the problem.

Any help, advice or suggestions welcome. I haven't added fertilizer
tablets recently so think I'll do that too. Maybe I'll poke in the
substrate a bit and see if I get gas bubbles around them.

George, seems to me you commented you hadn't had success with this
specimen even using the high-tech approach. *sigh*