sick/dead pleco

During the week i came in from work to find one of my zebs with a swollen stomach.
It is roughly 9-10 months old. Water parameters are fine. All other zebs are ok.
I havent fed them anything new or different.
I cant find any feces in the tank to say if it is white or stringy.
After closer inspection the plec is blood shot on top of his head, between the eyes.
The underside has a small verry red indent just below the mouth.
The left side of the belly is black and the right side is red (blood red )
Breeding is a little fast but not overly so. Still swimming but i dont give it much hope.
Water; temp 28.5c pH. 6.8 Gh. 6 kh. 4 Amonia. 0 Nitrite. 0 Nitrate. 2.5

The day after i found him like this and the day he died he had fungus coming from his Annis. This would suggest to me that he was blocked up, with a small piece of feces at the Annis that fungus-ed.
I did a quick armature examination just after he died.
As soon as i opened him up what appeared to be boil (like oily water) oozed out.
I looked at some blood under a micro scope. It appeared like it was 30% white cells, or gas/water. i just dont know. But it just wasn't right.

Ok after opening up a new test kit to double check my water everything is pretty much the same except the kH 50ppm-2.8dH and the gh 60ppm-3.36gH.
the test kit i was using wasn't old, about 3 months old. But we all know test kits can be wrong.
This got me thinking that the water was passably to soft.
After looking through a few books it seems it could be osmotic stress.
The idea of osmoregulation sounds most likely except for the hemeraging in the head. Unless the water retention caused not only the swelling but some sort of flux between the water and the blood resulting in the blood vessels swelling making them visible in the head as well as the body.
I am clutching at straws here so forgive me if it sounds ridiculous.
If it was osmoregulation or brought on by osmotic stress how could this have been reversed successfully?
I have read that increasing gH can cause a calcium build up in the kidneys resulting in death.

My first taughts on seeing the sick pleco was viral infection untill i seen the fungus then i taught it was bacterial and when i opened him i taught it was a dietary problem due to the blockage and what seemed to be like boil.
But now after re-testing the water i am thinking it's the water been to soft.

Here is a pic. of the head. He is still alive here.


Here is a pic. of the underside. Dead here. Some of the swelling has gone down. If you look closely you can see the fungus.


Here is a link to the slide of the blood and a pic. of him opened up. You can see what looked to me like boil.
s11.photobucket.com/albums/a171/platty252/sick%20zebra%20pleco/

How can i safely increase the gH without increasing the ph or using acids that would give me false readings of pH and kH.
I have added a verry small amount of crushed coral to my filter to raise it slightly for the moment.
Any ideas or suggestions. I would hate this to happen to some of the other pleco's.