My killie breeder tanks aren't very large, and I don't have so many of them that I can just keep moving each new batch of fry to a separate species grow-out tank.  I've tried the net-type fry compartments that hang inside the tank by hooks or suction cups, but they take up too much space in my small tanks.   I'd resigned myself to keeping the fry in separate, small containers and doing daily partial water changes---man, what a hassle that's been!  Then, during last night's round of water changes, inspiration struck: I could use my kids' Legos and some knee-high stockings to make my own, custom-sized, in-tank fry compartments.

You just build a square or rectangular frame in the size you want it out of Legos, then stretch the knee-high over the frame, secure the knee-high to the frame with one more layer of Legos, trim off the excess knee-high material, float that baby in the tank and add your fry!  The Legos are bouyant enough that the top layer of bricks will float above the water line, effectively walling your fry off from escape or intruders while still keeping the top of the compartment open for easy feeding access.  

If you need very small compartments like I did, you'll find that using pre-fab Lego window & door frames snapped onto a flat base panel makes a compartment sturdy enough to withstand having a knee-high stretched over it without collapsing.  Otherwise, a frame built out of the standard, two-dot-wide Lego bricks and beams will do just fine.  I'm such a geek, I even decorated my compartments with little Lego furniture, Lego houseplants and other accessories.   Not that the fry really need a chair...     :P

  That's so awesome!  I would have never thought of that!  However, I did put a little lego fort in my tank, and it's so cool!  It's very bouyant, but the lid holds it down.  I will have to try the lego fry home, though.  It's like a little daycare!