Hi Andrew,
I suspect that a sword that big might be a bit much for most peoples 'scapes. It prbably weighs ton as well so I'd probably break it up into individual sizes and as you say, reduce much of the leaves. As long as the rootstock is nice and white it should transplant well.
According to nutricalc a 200 liter tank gets a baseline scheme as follows:
3X Weekly
=========
5/8 teaspoon (3 grams) KNO3
1/8 teaspoon (1 gram) KH2PO4
On Alternate days
==============
1/4 teaspoon (0.5 gram) CSM +B or 11 ml Tropica Plant Nutrition
Judging from your sword size I would say you have plenty of plant mass and you could easily
double these figures. Personally, the only data I pay attention to in my water company report is the Calcium and Magnesium levels. I totally ignore the nitrate and phosphate readings and assume they are both zero. This is part of the EI philosophy because you simply can't harm the plants or the inhabitants by overdosing. I would definitely recommend buying the KH2PO4. Although I would NOT use the Phosphate buffer as a Phosphate source, I'm fairly certain that it was not the cause of algae when you were using it. You should use the CO2 as your defacto method of lowering your pH. At the same time you need to be certain
why you want the pH lowered. It's better to focus more on CO2 saturation and accept whatever pH that results in. If there is a more specific reason for wanting to lower pH, such as breeding certain fish, you can accomplish that by first lowering the kH by mixing in RO or distilled water into your tap. At lower kH's the pH will be lower at your target 30 ppm CO2 concentration.
For traces, I'm not familiar with Chempak, but it ought to be OK. Tropica Plant Nutrition is recognized around the world as an excellent trace mix. It's very difficult to judge one trace mix versus another because the effects are subtle, if perceptable at all. The Seachem line have excellent, if expensive products. Their "Flourish" is their trace element mix. You may also want to try their "Flourish Excel" which is a pretty good carbon supplement to tide you over while sorting out your CO2.
I've never been able to get wallichi pink when it's in a subdued area of the tank (it mostly goes dirty brown). If I move it to the brighter area of the tank it stays more or less pink (at least in the upper half) and the growing tips turn orange. Other may have a different opinion, but I'm not one to try N starvation in order to bring out red colors because it requires too much monitoring or the consequences are dire. I dose like crazy and find plants that turn red with lots of dosing. The theory driving the N starvation to bring out red is that Chlorophyl, being mostly made of Nitrogen is abundant in the leaf when dosed properly. The green of the Chlorophyl tends to overshadow the red pigment in the leaf if the plant is well fed. By restricting the Nitrogen dosing Chlorophyl production is lowered and the red pigment can "outshine" the lowered green. I would rather have plants that
produce more red pigment when they are more well fed. That way you aren't playing with fire. There are enough red plants that respond to good feeding, Alternanthera Reineckii for example, or some Echinodorus Cultivars, that I don't bother trying to induce red by marginal feeding.
Have you ever seen a red sword? This fellow sells Echinodorus Imperial which starts out green and turns red.
http://www.aquarium-gardening.com/individual_plants.php
Cheers,