Need urgent advice - common

[Complecs]

I have a common (Pterygoplichthys pardalis) pleco, 'he's now approx 12-13" long from tip to tip, and he's currently living in a 400l 4' tank with a few tiny inmates - he is king of the tank, and has plenty of bogwood and plants to hide in.
What's worrying me is just recently he's started pummelling around the tank really thrashing his (considerable) weight around and has 'crashed' a few times into the side of the tank - so he has a welt on the end of his nose where he has bashed it

I am fearing he has gotten too big for the tank, is it possible to rehome to a aquaria shop (for them to rehome appropriately) to sit in with their koi? or is he too small for that stage? I'm at a dilemma of what to do, but something certainly needs doing asap

water levels in the tank are all good and normal, temp 26*

[MatsP]

Looks like a crashing-into-something damage to me, yes.

As to when it's time to rehome a fish like this, that's always a bit of a difficult issue. I'm assuming your 400L tank is about 4' x 2' x 2', which means that it's suitable for fish up to about 12".

By the way, unless it continues to bash into things, it will probably heal nicely - unless there is something else like a secondary infection, or some such.

--
Mats

[Complecs]

I have to say what concerns me is why he's thrashing around the tank like that in the first place tbh, he's always been fairly skittish and shy as (I assume) he was bullied in the tank he came from originally by another CP he was housed with, but just lately he's gotten very much more skittish jumping at everything (even taking that photo was a challenge - as previously as soon as he saw the flash on the photo prior to the above image he rocketed across the tank. so that certainly seemed to take away the 'he's doing it because hes blind' suggestion I was previously wondering.

In fact the only option I can think of of when his bizarre behaviour started (but before it escalated to the level it's at now), is when we moved the tank. due to the size and weight of the tank, it was thorroughly drained and all residents popped into a life support bucket (huge flexi bucket with heater and air stone), the plec had his own bucket but it was a challenge getting him out and well he did make a jump for it (from not very high up), then had a carpet crawl before stinging my husband with his spines and then popped back into the water - since then he's had something of a heiracy complex, he's been much more active (for a plec), and much more confident in his tank, so the recent skits and bumping do really worry me as to their cause; anyone have any idea?

[MatsP]

Don't know. My large common [that I "inherited"] is very docile. When did you move the tank - is it possible that the water isn't quite as good as you thought.

--
Mats

[Complecs]

we moved the tank many months ago tbh, actually thinking about it probably closer to a year ago if I'm honest

I check the water in there fairly reguarly (we've got the little test tube water testing kit)
just done the test again this exact minute, these are the exact results:

PH: 6.4
Amm: 0
Nit: 0
Nat: 5

Tank is mature and been running about 3yrs at least now, external filter, decor kept dark to soothe the plec (read some years ago somewhere that they dont like it garish), plants - real, bogwood - real

inmates in the main are 18 barbs (tiger, green and black rubies) that leave him completely alone (if anything they run if he moves) and 2 apple snails
I had SDs in there before for a while but he 'hunted' them so they had to be emergency rehomed after a couple got nearly stripped