I have a similar size tank 7x3x3 that I just setup and a 3x3x1 grow out/timeout tank. I made the mistake of asking for advise and got flamed, rightfully so I went crazy with the stocking. But I am hard headed and dont listen. Maybe you can use what I have as a baseline. I do 20 percent water change daily and 70 percent once a week so I dont foresee having a issue anytime soon as long as the feeding is regulated.
Main tank
1 8 inch NGT datnoid 8 inches (Currently in 7x3x3)
1 Lince catfish 16 inches (Currently in 7x3x3)
2 Alligator gars both 12 inches 1 albino short body 1 platinum (Currently in 7x3x3)
2 long nose gars 12 inch each (Currently in 7x3x3)
2 Big spot BD stingrays 12 inch each 1 male 1 female (Currently in 7x3x3)
Growout
1 Liechardi Arowana 3 inches (Currently in 3x3x1 growout)
1 Albino chines perch 5 inches (Currently in 3x3x1 growout)
1 3 inch 4 bar sumatra datnoid (Currently in 3x3x1 growout)
3 Albino silver Arowanas all 6 inches (Currently in 3x3x1 growout)
3 phantom RTC 2 regular 1 short body. All 4 inches or less. I Will eventually end up keeping probably just the shortbody (Currently in 3x3x1 growout)
8 1 inch Sumatra 4 bar datnoids (Currently in 3x3x1 growout) planning on keeping the ones i like and selling the ones I dont.
2 Female BD 1 eclipse and 1 thousand island 6 inches each (Currently in 3x3x1 growout)
Basically if you get any variation of what I got im sure ppl will say tank will be overstocked but I think its doable and with everything fullsized will look incredible. I stoped short of a fly river turtle but I think that would be a nice finishing touch. Hopefully this helps with stocking ideas.
