Hi, I'm new here so hopefully this goes smoothly...

I have recently up sized my tank. Everything seemed to be going great, moved everything over, added more plants, everything started cycling rapidly, plants are thriving, fish seems happy, water parameters right where I want them, great...
Then..
Two days ago I thought to myself that my weather loach had been acting very illusive and lethargic for a couple days. She was feeding well, if a little slow on the uptake, but really hadn't been herself for a couple days, something I'd written off as maybe the novelty of the new tank wearing off.
I put my hand in so I could check her over, which would normally bring her straight to me, but no. Instead her initial reaction was to freak out and bolt away from me. Never done that before. She quickly came round and I was able to look her over. I found (and hopefully the photos have loaded) a small, ulcer like hole on her 'chest' between her pectoral fins.
Straight to my local shop and in with Esha 2000 and Optima. On day 3 now and although it certainly hasn't got visually drastically any worse or changed at all (maybe slightly larger though), and she doesn't seem to have gone downhill (in fact she seems a little more active (but not much)) I'm not seeing major improvement.
She spends her day laying around the tank, occasionally moving to a new spot, while her healthy yet confused tank mates check on her. At food time, the untrained eye may even say she seemed fine... But no..

Anyway.. sorry for the long one ...
But has anyone ever seen this before?
Hopefully the pics are ok. She's not the easiest fish to photograph.
Am I correct in diagnosing an ulcer (cause not yet known) or is it something else?
She's always been otherwise very healthy and active (except when she jumped down the back of a unit, into some cobwebs for 45 mins).. oh and she's 3.5 yrs old

Sorry for the late reply.
It does look to me like it might be an ulcer (although I'm not familiar with that species of fish), and you've been undertaking the correct treatment that I would have done (although I rarely find an improvement after 3 days and often have to extend the treatment by a couple of days and then wait for a few days to see if there's a latent effect/improvement).
As the water quality is fine after the move (presumably you moved across the filter media so there oughtn't to be too much of a swing in water chemistry), what may have happened is that she's struggling to adjust after the sudden change of environment incl less biofilm in a comparatively immature tank and consequently may have injured herself in the process such as darting around to try to get her bearings or hiding herself in strange locations (such a you've already described).
Personally, I've had some very good outcomes and complete turnarounds with Melafix in recent years on other fish (much more than I've ever had with actual medications), to my surprise and delight. I would have a search to check that it's compatible with your tankmates (eg I think surface breathers may struggle with it or require extra water-surface agitation).

Thanks for the reply.
And thanks more so for slightly restoring my faith in humanity!
I've posted this in similar forums and ... Well... Wow....
Reminded me why I've mostly come offline!
Barry from Batley and his mates 'need to know' all my water parameters and every detail of every plant etc. Etc etc..
And because they hate their wives they love to turn a simple question into an all out, irrational attack ?

Anyway.... Back on point...

Things have got worse .. well, they were worse.. I believe I'm on the road to fixing it.

Shortly after writing this post I noticed some white spots on my beautiful little weather loach... Which spread to other fish..

So..

I believe I know why.
(Ps. I am an experienced but clearly very lucky fish keeper who has never encountered disease or injury before!)

I put a tunnel in my aquarium... And I didn't check right inside .. a mistake I am now feeling extremely guilty for... There was a sharp burr!

My theory ...

She shot through the tunnel and caught herself on the sharp burr ...
This wound ulcerated...
This led to her being in pain and stressed..
She developed white spot..
As did most other fish ..

Solution...

I have been through the entire tank and removed all potential sharp points...
I have treated with Esha 2000 and Optima and exit...

White spot is now barely noticeable...her 'hole' is still there... But she's more herself..

I continue to treat... And this far, in my tank that has everything from a large weather loach to four little hillstreams... I haven't come close to losing anything..

We're winning!

Glad to have been of help, and thanks for the update.

Your theory sounds 'spot on' - and your treatment for it too. Well done!

Keeping everything crossed that this fully resolves and that your weather loach returns to her usual self.

[If of any consolation, I've also "been there" with a decor problem that only revealed itself after the event - it hadn't occurred to me beforehand; fishkeeping does seem to be very much a "live and learn" hobby.]