I have started with really small Loaches (first batch was just under 2", the next were closer to 1-1/2", or a bit smaller)
I quarantined and treated for parasites. One group I also treated for Skinny disease.
The Loaches that I have treated for parasites:
a) Lived. (No treatment = 90% death rate while in quarantine, 100% in the first year
. Treatment = 80% survival)
b) Grew fast. The oldest ones that I have started at just under 2" and reached 3-4" in the first year (doubled in size) and have grown to about 5" by the third year. They are playful, and very active. They make FULL use of the 4' long tank, and I have my 125 set up and am going to finish the decorating tomorrow. The Loaches will move in as soon as the water is clear enough.
I have (3) @ 4-1/2 to 5" and (5) @ 2", started as 1" or so several months ago- they have almost doubled in size, including girth, since I got them this Spring.
So... how fast do you need a larger tank?
If the fish have not been treated for parasites, then do so in the current tank. The other fish may have picked up the possible parasites, too, so all ought to be treated.
Watch the activities of the fish. Loaches can be a bit aggressive with each other, and the lower ranking fish needs enough room to get away. If the alpha Loach thinks the lower ranking fish has not gone far enough away (the tank is too small, or not enough hiding places) then the alpha may continue to harass the lower ranking fish, thinking that the fish is still challenging him (or her)
I would suggest that you plan on 1' of tank for 1" of the largest Loach, though you can keep several Loaches and other fish in that tank. The space overlaps.
My largest Loach is 5", and is in a 4' tank. I can see it is not as much space as (he? she?) wants. Plus, I am planning a specialty tank with a lot more than average water movement.
