SAE Stocking

It would help to know what other fish and how many you have in each of those tanks, for a proper recommendation...
 
I would not recommend putting SAE's in the 20 or the 36. They get rather large and are highly active. I have 3 in my 45 and feel like I am pushing it. JMO
 
I agree 100% with Noodles. I have 2 in my 75G tank and they grow very, very quickly and are very active fish! Depending on what else is in the 55G, you might be able to keep 2. They are definitely happier with another one of their own kind. Mine stay together all the time.
 
You absolutely can put 2 in that 55G then.
 
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