I need help with my golden nugget pleco who iv had for 6 months, when i got home from work he (or she) was upside down in a corner of the tank really pale with no movement.
Thinking the pleco had died i went to get it out the tank where it started slowly moving. iv placed him in a small 20 litre tank that id intended to keep shrimp in.
over the last hour his colors have come back but he is swimming around in circles hitting everything in the tank sometimes sideways/upside down.
I'm unsure of what may of caused the problem or how best to help fix it.
Fist two photos are from 3 days ago, then one from when i first put him in the small tank



Tank size 180l running for about 8 months
Other Fish in the tank are:
7 purple harlequin
7 Golden harlequin
6 Penguin Tetra
6 Lemon Tetra
2 Zebra Loach
Water parameters are:
For the 180l
Temp 23-25
pH8.0
GH 8
KH 10d-15d
NO3 50
NO2 0
CL2 0.8
20-30% Water change every Saturday
For the 20l
Temp 25-27
PH 8
GH 8
KH 15
n03 25
n02 0
cl20
Thank you
Luke