Summary : Our largest fish (18") hasn't been visibly eating pellets for a while (1-2 weeks). He's not closing his mouth fully.
![Image](http://www.merproject.org/~lbt/pics/koi/skullface.jpg)
We have a fair amount of plants in the pond and he has eaten them and algae from the walls in the past so we've been keeping an eye on his behaviour and not seen anything too untoward.
He's been as active as normal; swimming well and socialising. He does hang around a bit when the rest feed but doesn't move to take anything himself.
He's now showing signs of lethargy and we're getting quite worried.
The rest of the fish are eating really well.
He's got no visible signs of damage, infection or soreness and a scrape this morning showed no parasites.
(The scrapes are sparse as he's not got much mucus although he feels slippery and looks healthy)
This morning we got a proper look at his mouth which looks healthy too (ie not sore or ulcerated) but when we took him out into a small tank we saw he didn't appear to be closing it all the way - I looked inside but could see no obvious blockage.
I gently put my little finger in his mouth and he spat out what looked like algae but I couldn't feel anything else. Microscopic examination of the spit-up showed nothing moving.
![Image](http://www.merproject.org/~lbt/pics/koi/skullface_mouth.jpg)
Today (2 kits so some figures are duplicated)
pH : 7.2 / 8.0
Ammonia: 0 / 0.1
Nitrite: 0 / 0
Nitrate: 0 / 0
GH: 125
KH: 220
Chlorine: DPD4 rapid in 10ml: possibly the faintest hint of not-white but almost undetectable next to a reference clean water. Tap water goes very pink (First time we used this, thanks MS
![Smile :)](./images/smilies/icon_smile.gif)
Some background:
The pond is 12000litres with about 40 goldfish/koi. Most fish are 3-6" long with 4 koi at about 12" and one at 18"
We now know it's very underfiltered with just a small pressure filter but water quality measurements have been very good (see above)
The main thing we notice is that there's a lot of silt on the pond bottom.
A couple of months ago we began to research and design a new filter system.
Three weeks ago we added a K1 moving media filter as an additional biological filter stage.
We're in the process of doing some building works nearby (preparing to add a Dracodrum filter) over the last 2 weeks but with the skimmer we're keeping dust out.
Nb - the work has been mainly digging clay so it may have stressed the fish slightly but should not have contaminated the pond.
Three weeks ago we got Duncan's book and a microscope and used it to positively identify skin flukes which I treated with a single dose of Flubanol.
Around this time was when he stopped eating. Our vet was a bit worried about the flubanol affecting the other fish so we were especially vigilant for changes and it seems unlikely that we'd have missed a connection.
Anything else I can tell you?
David