Uaru and dats should be fine at a smaller size, and if raised to gether until adult hood, they should still be fine. I would get at least 4, i find with only 3, one is always getting picked on when the other two form a pair. But that wont happen till around the 4-5 inch mark. They are a sort of slow grower, maybe a half inch per month on average. I have 7 uaru and i find they will eat almost anything, but can be picky with pellets. Mine prefer Hikari excel, and Hikari gold sinking formula. The go nuts for hikari discus bio-gold and frozen boold worm, they also love romane lettuce, but male a mess out of the tank from it. I keep the water at warmer temps of 82-84. PH doesnt seem to matter that much as i have a ph of 7.6 with hard water. Mine dont like stong currents, and need lots of cover, so some driftwood and fake plants work well. I have added 3 airstones to the tank recently and they seem to enjoy them, as they all play in them constantly. I filter with an FX5 and have the out put nozzle in the middle of the tank with both spouts pointing to opposite sides of the tank and slightly upwards to cut down on the strong current. I also used dither fish with them when i only had 3, but there not really need after around 4 inches, as they become less shy. they are not needed at all if you have more than 3.. hope this helps!