I see you joined in September so a belated warm welcome to Neoprodigy's MFK world.
No, like yours my Pangasius sanitwongsei swam at all levels at times and would even take floating chunks of herring/smelt from the surface occasionally. I did notice though that they preferred deeper water.
My observation of where (the level) fish swim in the tank is often done so due to the presence of undesirable or aggressive/abusive fish swimming in the level they would prefer to swim in.
I use minimal lighting and ambiant window lighting for both my bigger tanks. My fish prefer that. I use only 3 thirteen watt cfl's 24/7 when not feeding or making observations. Other lights are turned on as I need more to observe and off when finished.
Like yours mine enjoyed the current from the filter return pipes. Arapaimas do also.
The first shoal of 6 when they reached the 36" size and swimming at the 8 to 9 foot depth level and circling chunks of fish was one of the most amazing sights. Although we all know they are catfish they mimicked sharks in every movement.
The reason I moved them out of the 15 was because they were eating the Central american cichlids (which was OK) but the one that died did so because he took in a 13" (measured) Paraneetroplus formerly Vieja, formerly Theraps, formerly Cichlasoma maculicauda. Then was unable to swallow it because it was too big. He was unable to expel it because the rays in the dorsal stuck into his mouth preventing him when he tried to spit it out. This resulted in killing the P. sanitwongsei and the black belt.
Oliver Lucanus of Below Water ( formerly Biotope in the 1990's) visited me from Montreal a few days later and climbed into the tank after I drained between 10,000 to 12,000 gallons out and he caught the 6 remaining catfish, and his buddy from a Nature programming show in Great Britain placed them into the big tank. Oliver got nicked badly by a pectoral fin of one of them and mentioned how it bothered him over the next few weeks when he was exploring for fish in South America, where he flew to when he left my house.
pic#1. One of the fish from the second group just caught out of the 52 and placed in a holding 520g waiting to be picked up by a hobbyist with an indoor pond. The fish in the picture was an unusually aggressive paroon. He also was smaller than the 36" ones I had.
pic#2 Oliver Lucanus in the 15k.
