Hmmm, I am not sure you could keep all three in a tank that size for 4 years. They would probably all be 30"to40" by that time. It would be kinda crowded. They could definitely fit, but swimming space would be limited. If you cut it tall as possible then you should be ok, but expect them to squabble more and more as they grow bigger and bigger. Catfish tend to tear each others fins in territorial disputes. Or at least all the big pims that I have owned do. It might work, but I'd say more like 3 years 4 is pushing it, but it might work. You would definitely have to hook some major filtration for those bad boys though. You could start off with smaller filtration like I did and slowly increase it or you will start to see ammonia spikes as they grow, they will outgrow the biofilters, and they will need to get larger and larger with the fish. I'd say you need about at least 20 gals of biomaterial per 36" fish. That's not the size of the filter that's just the bacterial housing materials. Adding sand and rocks will increase the capacity also, just remember that rocks should be large enough not to be swallowed within the timeframe they are in the tank. I go with rocks that are 8" in dia or larger, and playsand or pool filter sand. The two mixed looks really cool and natural. the 150 gal tub would work good for a filter just look in the diy section at some of the home made filters. I'd set aside 60 gals of wetdry area for those fish. For my big tank I am trying to go somewhere between 500-600 gals capacity for the filter alone. To include 250-300 gals of pot scrubbers.
