It honestly all depends upon the pictus and other inhabitants temperment.If you look at my old pics and old threads talking about this combo, I had my 2 foot achara housed with his "children", 2 4" pictus fish for over a year, maybe 2. The only fish he never tried to eat and actually protected from my old meanass flowerhorn cichlid. The pictus were housed for a few months with the pictus as well in a different tank. Sadly, as we thought we were protecting the "children" by moving them into a different tank when the rtc needed to be housed in the bigger tank with the achara, one pictus got tangled in the net (special type for spiny fish too). Other one died from something went haywire with the water conditions. My 11 year old oscar is very domesticated in that she's not too aggressive and never ate other fish, incl when we used to use feeders years ago. Just depends.
As for the filtration, I had a FX5 with an uv sterilizer (again an extra powerhead) on our 75g for a couple of years. It was awesome. Was never too much current esp since we could redirect easily the outlets. And this was for our smaller fish which we recently broke down the tank and put the fish in a 20gallon tank (with the largest aquaclear HOB filter, filters longer than half the tank!)
As for the brown algae, kind of embarrassing to admit, but I still get it time to time in my larger tanks. I noticed it today in the 54g that only has a fluval 404 and a flowerhorn cichlid; 125g as I cleaned out the smaller fluval the other week and took out some sand, disturbing the chemistry/bacteria balance; and the 265g that has my 2 big cats, the achara and rtc...30g sump, fx5, and big uv sterilizer...that thing has sooo many different colors growing on the walls, incl white, but also has the brown crap. Have to test that water soon as I took out all the sand in it 2 weeks ago and probably caused the ph to become too acidic. Brown algae has nothing to do with a newer set up tank. I've never had it until my more established ones, those being set up and not completely tore down for years, at least five. I mainly notice it when lilke I said earlier, the bacteria load or water chemistry isn't right. I stick to what I was told, and has been proved to me over the years: green algea is a healthy tank, brown algae is not....and NEVER use the algae destroyer medicine, or any medicine. After losing many fish unexpectedly, some of my long lived favorites, I went to my local pet supply store and told them what happened. Water was clear, conditions were right, no aggressiveness or bullying, yet fish were dying left and right. He, as the owner and seller asked if I used algae destroyer anytime within the past year. I did about 6 months prior. He then said it causes liver/kidney failure and eventual death months later. He said he cannot come out and tell me this stuff when I'm buying it unless I ask about the risks involved. They've proved to be very honest, and actually told me to never buy an undergravel filter as it's equilivent to fish "swimming in their piss", but he would sell me one if I wanted him too.
the syndontis species...we have had one now for a couple years, 3 or 4. While the rtc was "growing up", only a "cute" 2 inches, the freaking syndontis always had a bounty on the rtc. I seriously thought the syndo was going to kill him!! When I saw him tearing chunks out of the then small rtc fins and sides, I threw the syndo into the 125g and has been in there since with no where to hide. I didn't care, but has held his own very well. He's in there with our 11yr old oscar, 18 inch tsn x achara cat, 9-12 inch giraffe catfish, 3 large irridescent sharks (large meaning the biggest one is same size as the tsn x achara and smallest is about 6/7"), 11" pleco, 2 large tin foil barbs 6-8" (last of a schoal of 6, others were eaten by achara and rtc cat), and 12" bala. Now, with that combo, the small syndo has done well. he's prolly only 4-5", but stands his own ground as long as he's with much larger fish. Now, with my tank load, you see why I've such filtration. I'm actually considering putting the old 75g fx5 on this tank as well as I'm still not happy with the air flow. I had a bubble walll as you stated you have. Even spent extra money for the super quiet air pump. However, the walls cannot be kept with larger fish. They will either play with it constantly, bang into it, or try to eat it as my hybrid cat did a lot and had suction cups lodged in his mouth.