My tank dimensions are 31" Lx12" Wx12" D
Can i keep 3 Clown Loaches & 3 Black Mollies in this tank.
I used to keep Tetras & Catfish but i am now gonna change to these varieties of fish.
Thanks

Your tank would be 16 gallons, considering Clown Loaches can get well over a foot in length, and are generally quite bulky as adults the tank would be way too small. Mollies prefer brackish water to freshwater, but a small group would be ok in a tank that size, though it's probably the minimum size.

If Clown Loaches are to big for this size of tank what other quite large colorful fish could i put in with Mollies.
Thanks

Going back to when I used to keep tropicals..... a rough rule of thumb as to how many fish you can keep......
1" of fish per 12" square of water surface area.

The fish capacity of a tank is dictated by the amount of oxygen that the surface of the water can absorb - as above, about 1" of fish per 12" square of water surface area.
So, your tank, with 31" x 12" of water surface area, can hold about 31" of fish.
So that's about 20 x 1½" fish - or 10 x 3" fish - or 6 x 5" fish - etc....

Personally I wouldn't keep anything that'll grow to much more than 6" or at a push, 8", in that tank (Clown loaches can grow longer than a foot)

And if you go for a larger number of small fish, it's best to add them to the tank in 5s and 6s at a time (as opposed to 20 at the same time)

They can, in the wild, but are unlikely to go above 6" in captivity, no matter how big a tank they're in.

Could someone recommend a compatable fish with mollies

Guppies, platys