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Also an adult pacu will be close to 2’ tall and this won’t give them much room to move up and down once they are big.That is a good size pond and no doubt opinions will vary widely over what and how many fish or inches you can keep in there. IMO yes, you can keep others that you mentioned there in there too, but I am not going to say how many as it will depend on types of fish, age and hence size, water quality, filtration type and efficiency, etc, etc.
Red tails are human friendly and feed from hand at the side. Hence the rough guidance on depth for a fish that in that size of pond should reach 3ft or more itself.
one thing to remember about pacu however is their bony teeth, which are very good at biting through liner style ponds or any wires from heaters or pumps (experience unfortunately - electricity in water smarts a little).
Just wondering. This intex pond is taller. Is it 1. Still safe for fish and 2. Sturdier than the ones most people usually use? https://www.splashandrelax.co.uk/products/Swimming+Pools/Rectangular+Pools/Bestway+Power+Steel+Rectangular+Frame+Pool+Set+-+13ft+6in+x+6ft+7in+x+48in/4155266750Agree with the guys above. Good for fish that almost always stay horizontal. RTC often prefers to go vertical when begging for hand feeding. But I don't 2.5' height (which means only about 2' water depth) as a showstopper necessarily.
Still, your plan would be a good experience builder for yah, IMHO. You gotta start somewhere. Just don't be deluded that this will work out long term. Spiny and toothy fish like the catfish and pacu and giant gouramy will ruin your soft wall pond. Adult female RTC (the bigger RTCs) will prey on arowana and giant gouramy.
Long term you will need a hard-wall enclosure and rehoming / reshuffling as the fish grow at different paces to different sizes.