Waterloo,
Since P. altums are wild caught, the size is really dependant on what is collected!!
It is very unusual for them to be collected at a small size (dime/nickel) and therefore a 20l/5 gallon tank will not suffice for quarentine.
Unless you are bringing them in yourself, they should already be debugged and used to the water in your area so quarentining them may not be necessary.
I am in the process of putting together several orders and wild altums are available to me this month so I may just bring some in.
Just a note: If you are confident in the shop you get your fish from then quarentining really is not really necessary.
Now I know I will probably take a ton of heat for that comment, but I do not quarentine new stock that I bring in before placing it in holding tanks that may already contain fish...... and I bring in A LOT of stock every month.
I do quarentine the stock prior to making it available for sale tho!!!
One question to ask if wild altums should be available to you is...how long has the shop had them?? This will tell you the quarentine time that the shop has had them in.
Also most shops that do offer wild stock do NOT bring it in wild themselves, but go thru a wholesaler who has already acclimated the fish!!
HTH
CM