Hi Oracle. Welcome to the forum.
What you are seeing on your keris has nothing to do with it being a "poison keris". It is merely the pamor pattern which is being revealed by the use of lime after you cleaned the blade with coconut water. Generally speaking, after cleaning a blade like this it would be stained with warangan (arsenic and lime) to completely reveal the pamor pattern that was forged into the blade which would should extend over the entire length of the blade. While arsenic is indeed poisonous, its intended purpose is not to "poison" the blade, but rather to raise the pamor pattern and make it visible since arsenic blackens iron while leaving the nickelous material in the pamor relative untouched and creates a contrast in the colors of the different metals. But i would seriously question the validity of any keris ahli who would claim this was some kind of special "poison keris".
Tangguh is a method of classification generally reserved for high level Javanese keris. It was never intended to be used to classify common keris like this one and certainly not keris outside of Javanese keris culture. But even if this keris could be classified according to this method it would be very difficult to nearly impossible to give a good assessment based merely upon a few internet photos. Here is some more information on the Tangguh system that you might find helpful.
http://www.kerisattosanaji.com/keristangguh.html
That said, this appears to be a nice Sumatran keris in old, well preserved dress that would benefit from a real warangan treatment. Given that you seem to live in Jawa it should not be difficult to find someone who can do this for you at a reasonable cost. I would love to see more photos of it if you decide to follow that route.