The water is fine.
The tank he's in now (for about 3 days) is with our baby clown loaches and dats and some others (various juvenile fish other than a few platies and my angelfish) in our 75g inhopes that they'd get him eating plus the water quality is kept pretty perfect. That tank gets a ton of feeding of small foods daily because of the baby loaches.
The parameters on that tank are no1=0, no2=0 and nitrates=5. The pH is consistently 7.4. The TDS is around 160. I would be surprised if anything else is wrong with it since there's clown loaches in there, a SA leaf fish and some other fairly sensitive fish and they're doing great.
It's aquascaped with some mopani wood and pvc and plastic decorations.
Up until a few days ago he was in with our arowana and clown knife in a 125g. We don't test the water as much in there since it's only those two fish plus the fire eel at one time, but the pH is the same (that's what it comes out at in the tap and with all our tapwaters buffering it doesn't vary) and the nitrates are always below about 20. Obviously no ammonia or nitrites.
In that tank there was absolutely no competition for food because our clown knife only eats beef heart and the arow eats pellets + krill and sometimes steals some of the knifes beef heart but hates everything else.
That tank isn't really aquascaped, it just has a bunch of pvc for the clown to hide in and also the fire eel when he was in there. The arow doesn't exactly use decorations and the tank is temporary anyway, lol.
The only similarities between the tanks is that they're barebottom so we're thinking about moving him into sandbottom pretty soon to see if he'll be more comfortable maybe and try to eat. I doubt it will do much since he has plenty of hiding spots either way, but I guess it's worth a try. I'm not very optimistic since we had a peacock eel at one time that was in a tank with sand, no food competition, perfect conditions and it didn't want to eat either no matter what we tried. At least this fire eel is bigger and has a bigger mouth so there's more options as far as food, but he doesn't seem to care about any of it.